On my signature computer (#1) I had no problem for a while but around the time I upgraded to Cat 4.2, Alt-tab problem started. I uninstalled the drivers cleaned the registry, cabs, all ATi related files and reinstalled but it didn't fix the problem. I tried omega drivers but no joy. I did a fresh install of XP Pro w/SP1 with a fresh install of new at the time Cat 4.3 drivers. Problem persisted. Changed the motherboard from Abit IC7-Max3 to Asus P4C800E-Deluxe and CPU to 2.8C P4, did another fresh install of XP and fresh install of ATi drivers and problem went away. Then the promise SATA controller died on the ASUS and I had to RMA it. I was building another computer (#2) with the old Abit and P4c 3.0 so I put it into service as my AH computer using vid card from #1, fresh install on new WD Raptor of XP Home fully updated, fresh install of Cat 4.4. Problem returned. I've done so many fresh installs with so many different drivers that I can't determine cause and effect.
I've had the Alt-Tab problem on my sons old Gateway 1.5GHz computer since installing an Asus Radeon 9600XT.
Setting in bios? setting on card? fast-writes issue? bios/vid driver issue?, overclocking issue (can't be the Gateway is stock)? If any body see's the common thread, let me know.
Don't have the problem with AH2.