How do you change the boot sector for a system when the main OS is no longer there?

I am rebuilding an old HP 933Mhz Pavilion into a media server. I had one before, but took it down about 8 months ago. Anyway. It is now a 1.8 Celeron foxconn system with 384MB of ram.

The Hard drive that I have in it as the boot drive is a WD 500GB Caviar SE16. Will be adding a pair of 750 GPs next month that I have sitting around.

Anyway, the 500gb was a pull from my new desktop build and had three partitions on it. XP, W7 Beta, Linux (ended up not getting installed so it was empty). Rather than doing a complete wipe, I decided to use the XP partition as the boot os for the server. I don't want to get into a WHS versus linux versus unraid discussion.

Anyway, I couldn't boot into W7 as it doesn't have enough ram. I erased the W7 partition, reduced the XP partition. I currently have it allocated 40GB for Windows XP plus Nero 7 for backups, and the rest as a logical drive. Problem is that the boot sector still thinks there is a W7 partition and it is set as the default. I could just restore the XP partition using the install disks, but I would rather not if possible.

Any good free apps out there that will do this? I can't access the W7 boot sector under XP from what I have tried... just the old xp boot sector.

Worste case scenario, I guess I can't just reinstall Windows on it.

I considered WHS, but I like the gui drop and drag folders over what I have read is used in WHS. For my purposes, I really am only using it to store media as well as a back up for critical documents. I have Nero back it up on there to automatically back those critical files on the other drives weekly.

It is the 64 bit.

I will just try to try the restore option then perhaps. The reason I was hoping to keep the partition is that it is basically is a fresh build. I built my new desktop on it in March and have been using W7 64bit as my main OS. The only thing that I had on there was AOEs because it wouldn't work on Windows 7 64.

I am realizing now, it will just be easier to reinstall the OS.

On that note, do you think 40gbs is enough. I guess it is actually overkill now that I am thinking about. I think XP only takes about 3-4GB with updates plus nero and such. So perhaps I can trim it down even more to maybe 20gbs. Then again, I guess I could double it up as a game server perhaps for some of my older games. hmmmmmm. For instance, it might have enough juice to run a lan UT2004 dedicated server with bots. Not sure and I will have to test. I do run a dedicated server for a number of games, but it is nice to set up a local lan game from time to time.

Primarily it will just serve media.