For HD activity in Vista, I always do the following to a new install:
1) Goto Windows defrag and turn off its auto schedule
2) Open regedit, search for "prefetcher" and set the values of both superfetch and prefetcher from 3 to 0
3) Totally disable the "Windows Search" service
Some people dont agree the above make for a faster PC, but personally I don't like my computer doing "background" work when its idle, i'd rather it was just that, idle, not making my poor HDs little heads flick back and forth constantly.
With re: to your speed issue, thats more of a problem, once you have SP1 installed and all the latest updates (might wanna check for a newer BIOS too just to make sure) and the latest drivers for all your hardware, if things arn't working well, come back and we'll see if we can figure it out!
EDIT: Should also have said, (again controversial advice I know), if you have a seperate hard drive, goto your page file options and set it to windows managed on that drive, and disable the one on your main hard drive. Or if you have just the one drive (or at least logical drive) then make sure the pagefile size is set to windows managed. It may not the optimum solution, but it does at least ensure you dont end up with a thrashing situation.
EDIT 2: Also, if you have your SATA controller set to AHCI mode and your motherboard has an Intel chipset, ensure that you have the Intel RAID Manager/Driver installed (can get it from Intel.com, latest version came out a few weeks ago) as I have seen systems with problems such as the HD cache being disabled in windows because the drivers wern't installed.