Ween--
I switched to Mac in June after 20 years of PC (Apple before that). I have a 20" iMac Dual Core 2.0GHz with 2G of RAM.
It isn't all that slow compared to my previous 3.0 GHz HP PC with 1.5G RAM.
It's is quicker running Windows with Bootcamp than it is on the Mac side, but I've concluded that's just the way the Mac is, a little more laid back, taking a little more time for the small and pretty pleasures that really define the Mac experience. OSX is just better looking than any Windows OS. THis goes for Vista as well, which I installed a couple weeks ago on the Bootcamp partition. Worked fine and it's like, copying Mac with all the fancy graphics, though it is a little garish by comparison.
At the same time, every program I put my hand to in OSX was quick but slower than the equivalent program on the Win side. In addition, the Mac has the annoying habit of presuming lots of things about the way you work, or want to work, so you end up working the way the Mac wants you to, not necessarily the way you want to. This has advantages and disadvantages, as you can imagine.
Since none of the programs I actually use to do web design and site maintenance, graphic design, photo touch up, writing, etc. actually work on the Mac, I was in the position of going through several learning curves--one for a new Web Design and maint program, one for desktop publishing (InDesign for Pagemaker), one for simple graphics/photo touchup (iPhoto for ACDSee), Word for Word (the Win version is MUCH quicker and better than Mac), Quicken for Quicken/Money (again, the Mac version of Quicken is 1980s software, whereas the Win version is up to date and very quick, and so is Money), and so on.
After four months I had work to do and couldn't wait to go through all the learning curves, so I repartitioned my iMac 20" to be 160 Gb Windows, and 70 OSX. I now boot into Windows XP all the time, and every once in a while, when I want to see all the pretty icons and the pretty borderless windows, and all the rest, I punch the Option button and boot into OSX.
I still use Garage Sale to do my eBay sales, but other than that it's all Windows all the time. I'll probably try to do some things in OSX from time to time, but it certainly isn't better than Windows for most tasks that computers are good for. Not for graphics, film, photography, design, writing, etc. Apple has an enormous advertising and PR machine and they make handsome machines and a handsome operating system and plenty of quality programs. But better? Maybe it's more like just as good.
So Bootcamp your machine and reinstall all your Win stuff on that partition, and see if that doesn't solve your speed problem.
Cheers--