My Win. XP has a virus that doesn't allow installing, I want to format it

What computer have you got? Have you checked to see if it has a recovery partition?

Why do you say it is a virus? what happens when you try to install? what are the programs you tried to install?

usually windows XP CD will give you an option to repair if you boot from the CD . No need to buy a seperate CD to repair

becarefull what you buy on ebay ,do you have a friend or family member that has a copy of winxp[must be same version as yours ] you could borrow and use, just useing your key to install winxp

It's a windows xp, don't know what recovery partition is.

It has a virus because I installed programs(they're gone now) on it with no anti virus & since that I cannot move things in the desktop or get them open from double clicking(I have to left click) but that's not really a problem although its part of what the virus does; I also can't install anything, it says something like "the windows installer service could not be accessed, this can occur if you're running windows on safe mode, or if the windows installer is not correctly installed"
I'm not on safe mode. Before installing those programs I talked about, none of this ever happened.

I don't have any CDs that came with the computer, that's why I'd have to get them through eBay

You can download Kaspersky virus removal tool. or Avast or anything. Then go to safe mood by pressing F8. And install Kaspersky virus removal tool(free) or Avast free. Scan for viruses in safe mood. It should fix everything. Then intall a proper anti virus.

OR

you can go to safe mood and try to restore your computer to an earlier state(to a date you didn't intall that program yet). Not sure if recovery is enabled. If disabled,you can't do it.

I am telling you to go to safe mood and scan for virsues using kaspersky virus removal tool or anything good.

you don't need ebay or other CDs. just internet

How you know that your system is infected If you have some dought that your system is infected by some kind virus so i advice you to install antivirus on your system and run a full scan with antivirus remove infected files your system will be safe you also get help from the " Antivirus Service " of your antivirus