Yes, these can make a real difference to your frame rate for FS9 or any other processor intensive app such as games. I personally use the freeware program "EndItAll2" (you can get it here http://www.all-freeware.com/EndItAll2.htm or lots of other locations - try a Google search if this link doesn't work for you). I have used it on XP and XP64 bit with no issues and typically see about a 10% improvement in performance.
Very easy to use, although it only allows you to save one set of settings, i.e. you can't have different profiles for what should be stopped for different scenarios.
There is also "FSAutostart" available at Avsim (free login required) http://library.avsim.net/esearch.php?CatID=fs2004util&DLID=57040. Not used this myself, but as well as the ability to stop programs and services like EndItAll2 it can also be configured to launch specified applications before FS which might be useful if you fly with add-on programmes that need to be started seperately. Also claims to include a memory defragmenter and the abililty to restart the stopped programs and services to bring your computer back to it's original state when you leave FS. In fact it sounds so good I think I'll give it a go myself tonight!!!