I've seen similar cases in the past. A virus would remove the boot sector and boot files on the root of the C:\ drive.
Sometimes it would go a bit further and remove the files from c:\windows\system32
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Always do a backup to all your documents before attempting a repair!-----------
There is a non-destructive method that you can try using tools that you already have, on this case you only need the windows XP install CD.
- Boot from this disc, choose the R option to repair the system (it should open the recovery console)
- Type FIXMBR
- Type FIXBOOT
(more details here:
http://pcsupport.about.com/od/termsf/p/fixmbr.htm)After these steps, reboot your OS and start from the disc again.
Now instead of selecting the "R" option, you should continue forward and before you start installing windows there should be a dialog box mentioning something like "Windows is already installed on this machine, do you wish to repair it?"
At this question box you should select the option that allows you to let the windows disc attempt a repair install.
If you don't see the second repair box and windows only mentions something like "Windows will now start installing" then it means that no windows OS was recognized as being installed on your system and therefore you'll need a full install from scratch.
On this case, I'd recommend wiping out the partitions to start from a clean state and then install.
As warned at the top, only do these actions after a backup. If you don't have a safe boot disk then you can download knoppix or similar
(link on the bottom of this topic)-------------------------------
This method should give a fresh breath of life to your windows install but beware that is not a 100% foolproof process. On some cases I've noticed that windows was badly corrupted and a repaired install was not enough to restore a good looking OS.
If you need badly to recover your documents and you're having troubles in building a windows based boot disc, then I would recommend trying out a linux based image which are legal to download from the web:
http://www.knoppix.org/