Thats a comman error and can be given from various things, main one is a failing HD but unlikely. First run a chkdsk from windows to fix error automaticly then hit yes and restart, let it go through chkdsk once to see if any new errors are found and fixed. If not then you need to establish some HD performance tests to see if the drive can pass every benchmark.
Next thing I would ask is do you have SMART enabled from the bios? SMART is basicly a monitoring device that is done through the startup procedure and diagnostics of the HD, any bad info or failure during this startup with SMART enabled will send the report back to the monitoring device in the software on your computer. If anything happens you will be given a update to the problem and thus can correct it or know your HD is failing enough that you should replace it. SMART only works on newer HD, I think 2001 and up. When you enable SMART in bios and the software is installed on your computer you will be given an update of any problems.
If SMART finds nothing then disable SMART as it increases the load times of windows and next you will want to check your motherboards battery, reason to check battery volts make sure its in spec 2.75-3.3v and if not change the battery out and see if this fixes the disk read error. Cheap purchase of the battery around $2 or so, no loss there.
Next thing that I know of this error is caused by people installing windows XP on a new SATA hd thats new for the first time and using NFTS partition. This error can be what is a serious problem between the WIN XP and bios addressing, at which a small known bug can cause a disk read error when the hd is new and installed using NFTS, so to correct this the HD should be partitioned into FAT32 first then gone back and repartitioned to NFTS and install win xp then. Don't ask me why this does this because I only remember this being one the reasons behind disk read error, maybe look up to see and try get a clearer answer as im just pulling out of my head old disk read errors and why.
Also go into bios and make sure the disk is shown in bios, it should be showing on startup, if not try to update a new bios or uninstall the last WINXP update if you remember this error right after a WINXP update because of that known NFTS FAT32 hd error that I tried explaining above.
Also boot to your WINXP cd and go to the repair console, try a /fixmbr or one of the help fixes on repair console, I havn't had to do any of that for a long time so im not 100% sure on my memory on the actuall commands but I know of /fixmbr is one them. Remember while you can get into windows, backup your data thats important while you might have the chance to before proceeding.
Well nothing more I can think of, other then the bad which is HD failure, sorry man hope you get it fixed, I know I hate crap like that.