Do softwares that claim to tune up your pc actually work? if so what are some good ones that can speed up my pc

some of them actually work, but usually at the expense of some services being disabled, or something like that. I usually don't really trust those apps, unless it's known to be good, and customizable (like, you know what you're tweaking). Because I remember this one time that I used some tweaking utility, to find out that I couldn't see the login screen anymore. So just be careful

Generally I've found that what most of these 'tune-up' utilities do is clean up your registry, get rid of invalid entries, shortcuts that go nowhere, tracking cookies, and so on. Clutter, whether it is cookies, spyware, malware etc. makes your PC run slower and some spyware mucks with programs too. So your first line of defence (after firewall and AV) for care is having a decent Ad-aware type program and run it often.
I have Tweak Power Pack '05 as my clean-up/tweeking utility and it seems to do a fine job at keeping things organised. It has a good set of features which include a decent un-installer, registry cleaner, access to your programs Add/Remove, a RAM idle feature (which I don't use), and good system monitoring (from memory to battery), and more.
When choosing one of these utilities, especially if you're trying a trial version, make sure it comes with its own un-installer since getting rid of one without it can be a real pain.
Go to Download.com or some such and shop around, and read the reviews to get informed of any possible problems. Almost everything at Download has been reviewed in one form or another. This is the best advice I can come up with right now, I'm sure others will have thoughts on this too, cleaning and tweeking etc. Hope this helps and welcome to GNz!
Quick edit: Lol, psYchotic is on the same page, he is quite correct about being careful as I too have had a couple of foul-ups using these utilities, iow don't mess with what you don't understand esp. your registry and start-up menu.

I usually don't like using software. Some of it does work ( http://www.tweakxp.com/ - Tweak XP is a VERY good program), but I like doing things manually. If you read up on my Guide to XP/2003 Tweaking, I have posted all the manual steps to tweak out your system.

Carefull though, some PC Tuneup software is actually pure-blooded spyware.

The only tune up software i use it Tune Up Utilities 2004. Its very eficient and it primarily cleans up invalid registry entires and temo files on your computer. Ive found it to be very efficient

Most don't do jack in my opinion I stay away from them just because they could be spyware.