This problem looks like a problem of ur bootloader, GRUB , when your windows xp checks for consistency it rewrites the MBR (master boot record) and wndows can't read ext3 (linux partition) hence u r unable to boot in to linux.
First of all try to reinstall GRUB( grand unified bootloader) at the time of installation select advance boot loader configuarion
Advanced Boot Loader Configuration
In Grub you can also determine where you want the boot loader to be installed. You may install the boot loader in one of two places:
The master boot record (MBR)
This is the recommended place to install a boot loader, unless the MBR already starts another operating system loader, such as System Commander. The MBR is a special area on your hard drive that is automatically loaded by your computer's BIOS, and is the earliest point at which the boot loader can take control of the boot process. If you install it in the MBR, when your machine boots, GRUB (or LILO) will present a boot prompt. You can then boot Red Hat Linux or any other operating system that you have configured the boot loader to boot.
The first sector of your boot partition
This is recommended if you are already using another boot loader on your system. In this case, your other boot loader will take control first. You can then configure that boot loader to start GRUB (or LILO), which will then boot Fedora.
On the other hand if you want to start installation from the scratch install in a sequence (1 window 2 Linux).
For more check this out
This HOWTO will tell you how to use the GRUB bootloader to turn your computer into a Windows + Linux dual boot machine, without affecting your current Linux installation.