Sasser is an older infection that has not been around in some time so you are dealing with more serious malware.
Ive tried repairing windows by booting off the XP Pro disk to no avail.
If you cannot boot up and cannot repair, then your options are significantly limited.
Some types of malware can result in a system so badly damaged that a Repair Install will NOT help!
. Reinstalling Windows without first wiping the entire hard drive with a repartition and/or format will not remove the infection. The reinstall will only overwrite the Windows files. Any malware on the system will still be there afterwards. Starting over by wiping your drive, reformatting, and performing a clean install of the OS removes everything and is the safest action
In case you need help with this, please review "How to partition and format a hard disk in Windows XP
These links include step by step instructions:
"Clean Install Windows XP
"Reformat & Clean Install Windows XP or Vista
"XP Clean Install Interactive Setup
If you need additional assistance with reformatting, you can start a new topic in the Windows XP Home and Professional forum.