No problems here in Vista 32. Uninstalled 7.2 (i know, i skipped a month), reboot, install 7.4, reboot. All is well.
As for ATI drivers in gerenal, ive never had any problems with them. I have been running ATI cards for about 4 years now.
You don't need to uninstall under Vista before instaslling the new driver. ATI/AMD (which one I'm not sure) has redone the whole installer to make it more efficient so all you have to do is click on the driver you downloaded. It'll ask you if you want to: uninstall drivers, replace it or fix a missed installation/corrupt driver. Choose replace previous driver and let it do it's thing. Then restart when asked for and you have a perfectly install driver.
That,s if 32 and 64-bit drivers install the same way, but I think they do.