Using the boot.ini entry that kaustav_geek gave me didnt work at all. Looking up stuff on the internet, i found out that boot.ini does not support more than 4 partitions. So, I tried setting rdisk(1) and disk (1) [I got the idea from what I know about RAID and it's configuration I learnt in college this year. XD Wow... education did make a difference. XD ]
@sakumar79 Looks like we both had the same idea in mind, but it didnt work.

And yes, all my 5 partitions are on the same HDD
Next thing I tried running a recovery console thingie... with "bootcfg /rebuild" but it did not help.
So, as a last resort, I used my XP 64 installation disk. Running a repair from the installation disk of WinXP 64 fixed my boot.ini file.
Thanks for your input though, guys!
Oh, incase you guys are wondering, my boot.ini file now looks like:
Code:
[boot loader]
timeout=5
default=multi(0)disk(0)rdisk(0)partition(1)\WINDOWS
[operating systems]
multi(0)disk(0)rdisk(0)partition(1)\WINDOWS="Windows XP Pro" /fastdetect
multi(0)disk(0)rdisk(0)partition(2)\WINDOWS="Windows XP Professional x64 Edition" /noexecute=optin /fastdetect
I guess the second OS partition is always set as partition (2) in bios, no matter what it's drive letter / physical location is on the HDD.
Closing notes: Time taken to bring my system back online: 7 hours. Including breakfast and a 2 hour nap, and two glasses of lithchee cremosa.
Stuff I tried:
Shifted my internet connection to the other PC. Found replacement boot.ini and other associated files. Tried booting from those from a USB drive. Did not work.
Paniced. Posted here. XD
Shifted my HDD to my other PC. Manually placed boot.ini file and other associated stuff into C:\ Only one OS worked.
Messed with boot.ini a bit more.
Gave up hope of a simple solution.
Ran repair from installation disk.
Did a small victory dance.
Made last spam post here.
P.S. I love these forums. I don't need to be a regular member here to get abuse-free advice.
Thank you all. Please close this thread as my issue has been resolved.