Also check to see if you have a page file enabled. I disable mine just becuase I have plenty of RAM to cover everything. Next thing is yes, check for viruses and I also suggest using CCleaner. It's an optimization tool that can help you streamline your startup programs and get rid of some of the junk just lying around bogging things up.
OH! and another thing, norton and mcAfee like to hog system resources as well if those are the anti virus software programs you are using.
But with 1 gig of RAM you should be able to run Vista fairly well, from what I can tell by how your describing how slow your computer is going you may also have something else wrong. I do not think BHD should be lagging on a Vista machine even with 1 gig of RAM.
Also telling us your system specs would help a bunches
