My system:

Dell Studio 540, Core2 Quad 8200 @ 2.33, Intel G45+ICH10R, PCI Express x16. 6GB RAM.
ATI Radeon HD 3450 (0x95C5), Realtek HD Audio.
Samsung HD642JJ and WD Caviar Black 1TB SATA
TS-H353B TSST DVD ROM and PLDS DVD+RW DH16A6S optical
Dlink WDA-2320 Wireless and Realtek RTL8168C(P) Ethernet

BIOS v 1.0.7 settings: SATA, USB Legacy

NB: If your hardware varies from above, you obviously will need to evaluate whether other kexts would be appropriate for the individual hardware.

I installed on an otherwise empty GUID 2nd HDD after Win7 was installed to first HDD.

Step 1: Prepare modified retail dmg from working Leo install:
Download important files:
http://rapidshare.com/files/368797667/Archive.zip.html
MD5: 5A3164DAD14E23365692A601A9E5B345

Step 2: Create RW dmg on desktop

Modify with IOATAFamily kext (solves problem: successful installer boot, but no drives detected by installer)
Restore to GUID formatted >= 8GB USB drive
Copy additional files from download to folder on USB drive (kexts [vide infra], kext utility, Chameleon v2)

Step 3: Boot from USB, run Disk Utility, and format HDD GUID with partitions as desired. Install.
(Custom install, base system only; on reboot, you may have trouble with USB device detection; unplug and plug back in and/or change USB ports (only my front two worked) to get KB/mouse. This gets fixed below.)

Step 4: Modify installation

Install kexts by dragging to kext utility:

1. EvOreboot,NullCPUPowerManagement,SleepEnabler (Allows sleep/wake)
2. IO80211 kext (for your wireless adapter! Attached is the one for my Dlink 2320, but if yours is based on the Atheros chipset, should be able to change the device ID in the plist.)
3. VoodooHDA (sound for my board, not perfect but works)
4. natit_x2000 kexts (video, not perfect but works)
5. IOPCIFamily (great USB fix; stops annoying failure to mount USB devices and only using USB 2 ports, as well as "Restart still waiting on AppleUSBUHCI" on shutdown and a variety of USB errors on startup) - big props to slice for this kext!
6. fakeSMC (eliminates need for DSMOS, decrypt) - further props to netkas for this one!

Modify Library/Preferences/SystemConfiguration/com.apple.Boot.plist for boot flags: <key>Kernel Flags</key>
<string>"Graphics Mode"=1920x1200x32</string>
<key>Kernel Flags</key>
<string>-v</string>

Install PCEFI 10.1
Install Chameleon

Step 5: Reboot and you should be home.

I was able to upgrade to 10.6.2, just didn’t install the wireless updates (breaks the atheros kept for my wireless adapter; YMMV).

What I got:
Fully functional 10.6.2 including WiFi, sleep (though monitor screen does not turn off), awakens fine and reboots without “Restart still waiting on AppleUSBUHCI” on shutdown or USB errors on startup, sound.

I’m a relative noob, so if anyone (everyone?) smarter than me has suggestions, things I did or didn’t do/need to do/need, please post!

Hope this helps the Studio 540 crowd.