First, u'll need a bootable cd/dvd of WinXP and a Win98 bootable floppy/cd/dvd .
Then, boot using the Win98 bootable disk.
Goto the installation drive/disk of Win98 and run setup.exe
After the installation is complete, if u don't get the dual boot option, then restart the system, boot using WinXP disk.
After booting, when it asks if u want to repair u'r windows or enter recovery console, enter that option.
It will ask u admin username & password.
After entering the required data, it will show u a command console.
Here enter, "chkdsk /p" (without the quotes) & press enter.
After it is done, type "fixboot" (without the quotes), press enter, then [y], then again press enter.
After this type "exit" to exit the console.
Reboot & u should be all done.
If u succeed or fail, then post a reply.