win7 and win-xp dual boot hal.dll and other problems

hi, a friend of mine has the following at first solved but repeating problems with dual boot system on two separate harddisks/partitions: first installed windows-7 x64 ultimate and after that win-XP-Pro sp3 on second harddisk. after solving the non-booting w7 with easyBCD writing win 7 bootsector to MBR and setting xp boot from the 100mb system partition, given a driveletter under w7. after that, hacked the register to prevent win-xp from deleting w7 systemrestore points. all succesful. later, xp would not run anymore with a missing or corrupt hal.dll message. solved that with help from this forum by rewriting win7 bootloader to MBR with easyBCD 2. a week later, both win7 and win-xp started doing a unwanted CHKDSK routine when not cancelled, at boot. very annoying. solved that too with this forum, thank you. after THAT, a few days later, the hal.dll error returned on xp boot. solved that again with easyBCD. but these problems should not be returning every other week, very annoying indeed. does anybody know what causes it and how to solve permanently?
help much appreciated!

Hi, my friend does now not get the Hal.dll error anymore, but now has a error "NTOSKRNL.EXE corrupt or missing"when XP is booted first. when w7 is booted first or after xp and then xp again, no problem occurs.....
have previously restored w7 bootloader with easyBCD.

thanks for the encouragement, but it would be helpful to learn WHAT methods you used to get it working!