registry cleaners?

I have downloaded and tried several registry cleaners and they all claim to clean vastly different numbers of entries? One would remove 67 entries while another would remove 255, ect.

Additionally, If I ran a registry cleaner, uninstalled it, reinstalled it, then ran it again, it would find all the same entries again. If I removed them the first time, shouldnt they be go forever?

I guess what I am asking is why is there such a huge discrepancy between how each registry cleaner functions.

it has lots of virus, spyware lots of junk
please list softwares I can use to fix my windows vista, & make it run faster. it is running very slow.
thank you

I use an Compaq Presario SR1103WM when I'm at my Dad's house. We've had it for about 2 or 3 years, and used it for everything from games to internet to whatever you can think of. However, it's outdated now, but I can't afford any major upgrades or to buy a new computer right now, so I'm trying to figure out how to run it better. The only specs I know are:

248 RAM (8mb is diverted to video memory) max is 1 GB
Intel Celeron(P) 325 2.56 GHz
40 GB HD

I have no clue about what the video card is, I've had it 3 years and still can't figure it out. Sorry the specs aren't very informative, but you could probably Google the rest if you need it. Right now it's on a dial-up connection, which I only use for instant messaging. Like I said, as of right now I can't really afford to upgrade it, but here in about a month I can. We're also getting Road Runner for it, which should speed up the internet connection a bit. Besides upgrading it, what else could I do to make it faster?
Also, I have deleted a lot of old software that I don't ever use anymore, and I just figured out how to clean the hard drive, so I did that for the first time in 3 years and it is sped up slightly.

My computer has been really slow and acting really weird. I've been looking for a free download that can scan and fix my computer. I've seen some online, but they only fix my computer to a certain point and then I'm required to buy the software to compleatly fix it. Anyone know of anything that is 100% free that works?

Everything I click on is real slow, and I have high speed internet, should I do a registry clean up, and if so, how do I perform that action?