I've been trying for a while to get OS X to run on my Dell Inspiron 1525. The following walk through I found on antyalias's wordpress blog helped me out immensely!

http://antyalias.wordpress.com/2009/05/27/hackintosh-10-5-7-running-on-dell-inspiron-1525/

There are a few additions/revisions I had to add to the guide above. Make sure to review all the steps before you actually start installing...

0. Very Important! Go and buy a copy of Apple OS X before you go through the rest of these steps. It's only fair to the guys over at Apple since you'll be running their software on your laptop ...or at least trying to run their software - haha!

1. Get a copy of iPC 10.5.6 and burn it to a DVD.

2. Download Dell_1525_Driver_Update_2009_05_27.zip and save it to a flash usb drive.
http://hotfile.com/dl/4015785/3a47b7d/Dell_1525_Driver_Update_2009_05_27.zip.html
Please email me if this link dies and I can upload it somewhere else for ya.

Update 1-16-2012
The above link is no longer active, go ahead and try this one instread:
http://www.mediafire.com/?dzbwo74g22vb1pn 

3. Download Mac OS X Update 10.5.7 on apple site and save it to a flash usb drive.
http://support.apple.com/kb/DL826

4. Plug in a monitor to the VGA port and make sure the monitor is on during the install.

5. Boot from the iPC DVD and press F8, type -v. Lots of messy text will appear and you'll see code running. While the code is running, tap Fn+F8 so that the code shows up on the monitor instead of the laptop. When the install is ready to begin, the screen will go back to the laptop automatically. This took about 5 minutes for me so be patient!

6. Open Disk Utility and format your drive to Macintosh Extended Journal and name it Macintosh HD. Erase and continue.

7. View the option for Customize and select only these packages:

>Select iPC OSx86 10.5.6 Base System 6.3 GB

>iPC OSx86 10.5.6 Intel AMD SSE2 SSE3...
>>Drivers...
>>>Chipset Drivers...
>>>>Select Intel ICHx SATA Drivers 132 KB

>>>USB Drivers...
>>>>Select Patched USB Drivers 2.9 MB

>>>Power Management...
>>>>Select Clamshell Display Support 36.0 KB

>>Fixes and Patches...
>>>PS/s Device Support...
>>>>Select PS/2 Keyboard Fix 1.4 MB

>>>DSDT Patches...
>>>>Select Patch DSDT 628 KB

>>>AppleSMBIOS Patch...
>>>>Select AppleSMBIOS-27 Rev6 MacBook 52.0 KB

>>Applications...
>>>Select Kext Helper b7 3.8 MB

8. Install and Restart. Then remove the iPC DVD

9. Boot from the hard drive. Your screen will go blank after apple logo dissappears. Wait a minute... really, wait 60 seconds. Make it 75-80 seconds to be sure.

10. Perform "The Sleep Trick"...
Unplug your power cable. Close the lid screen. Wait until hard drive light idles (this means no fast blinking). Then open the lid screen again. Your screen desktop should appear. Don't waste your time, setup your information (SEE !!NOTE!!).

!!NOTE!!: If this does not work for you (it didn't for me!) you will be asked to restart. Go ahead and do restart. THIS TIME when the laptop is booting, hit F8 to get the boot options... then tap Fn+F8. This will swap the text on your laptop to the monitor. Now you can continue normally with the boot. Repeat the steps above for "The Sleep Trick" and you should be able to get to the desktop.

11. Drag/copy the dell drivers and 10.5.7 updates from your flash usb drive to the desktop.
A. Open the sleep trick folder & drag dsdt.aml to Macintosh HD. this will fix the blank display on your GMA X3100 graphics card. Now you won't have to use the sleep trick anymore (well, I still have to so this is something I still need to fix on my computer).
B. Install chameleon for fake boot interface. Restart.

12. Install the 10.5.7 updates package that's on your desktop. Open the disk utility and repair permissions. Restart.

13. Install other kext and package inside dell driver pack.
* Install Wifi broadcom package
* Install Power Management
* For audio. Drag 1525_Codec to AppleHDAPatcher_v1.16
* Install Samba if you want to share files with other windows computers on your network.
* Install SD Card Reader using kext helper.
* Open the disk utility. Repair disk permissions. Restart.

That's it! Enjoy your hackintosh!

Depending on your setup, you may have to go through some of the same extra steps I had to go through. It helped me to have an extra monitor to get through the sleep trick. For some reason I just couldn't get the video to show back up on my laptop. Also, I forgot to run the disk permissions repair at one point and so I had to boot to the install DVD, run the repair, and then try booting again. Kind of a pain but worst comes to worst and you can start over from the beginning.

The install disc I used was iPC 10.5.6 and I was able to successfully upgrade to 10.5.7 but my Ethernet connection didn't work anymore. Also, I have yet to find any compatible drivers for my Intel wireless card. I've been wanting to get a compatible card but I don't really need it i guess :) So far things are running pretty smoothly on about 3 GB of RAM. One of my main goals was to get GarageBand to work on my Dell... mission accomplished!

Here are some more pages I found useful in my OSX86 quest:
http://tgrounds.blogspot.com/2009/04/leopard-os-x-1056-on-your-pc.html
http://mintywhite.com/vista/triplequadboot-pc-windows-ubuntu-mac-osx/
http://www.amazon.com/Mac-OS-Version-10-5-6-Leopard/dp/B000FK88JK
http://www.amazon.com/Apple-MB966Z-A-iLife-09/dp/B0014X5XEK
http://www.google.com/search?hl=en&q=ipc+10.5.6+download