why do their updates always make my computer run more slowly?
There are several things that you can do to speed up your computer, most of them only if you know what you are doing.
I use CCleaner to clear off temp files. You can use the registry cleaner in it, but things like that generally can introduce their own problems
You can also use a registry defragger, that can speed things up a little.
Also a general file defrag ever now and again.
What I do when a Service Pack is released (ie: SP1, SP2 or SP3 etc) is roll it into the install disc and re-install windows fresh. Much better than an ancient install with a few service packs tacked on here and there.