Major boot problem!!!

Ok, i'll try to lay this out the best I can. I have an HP 6407 desktop with Vista OS. I bought another hd so I could try out the new Win7 beta. I partitioned the new hd with an XP disk I have so I could have 2 primaries. 1 for Win7 and the other for XP. So Win7 installed with no problems. Everything is ok so far. I can choose which drive to boot from by hitting the esc key during boot. The boot menu allows me to boot from my original 360gb hd with Vista or 500gb hd for Win7beta, or even allows me to choose to boot from CD.
Both Vista and Win7 booted fully when chosen. Now here is where it when bad I think. The extra partition on the new 500gb I was going to install XP. So when I was finished it would only boot from XP partition. So I unpluged the new hd with Win7 and XP, so now when I try to boot from the original hd I get this messege..."WINDOWS COULD NOT START BECAUSE OF COMPUTER DISK CONFIG PROBLEM. COULD NOT READ FROM THE SELECTED BOOT DISK. CHECK BOOT PATH AND DISK HARDWARE...." I don't know squat about mbr. Actually this was the first time I used XP install disk to partition a new hd.
PLEASE IF SOMEONE KNOWS WHAT TO PLEASE SHARE YOUR INSIGHT.

THANK YOU FOR YOUR KIND HELP IN ADVANCE.

 

Your problem have VERY SIMPLE solution.NEVER install new OS before old.Now reformat again,and install the OS's like this:firstly-XP,then-vista,then-Win7.Now you will have triple boot,and on the boot screen you will see boot choices e.g:earlier windovs versions,vista and win7.
GOOD LUCK!!

 

Amen, couldn't say it, any better

 

Thx for responding. That's good info to know. Just to be clear, this was'nt a project where I install three different operating systems, one after the other. Vista (on the 360gb hd) has been my primary os on this machine for a year now. The 500gb hd I aquired to try the win7 beta. Installing XP was an afterthought since I had alot of extra space. Is'nt there some way to recover the boot record for Vista? Everything else looks to be there when I view the Vista drive from XP. Also I'm trying to understand how installing XP affected my 360gb hd with Vista since it's physically on a separate drive. I think I get it affecting the Win7 because it's on the same physical hd as XP. But maybe not cause Win7 and XP are on separate partions,(These are sata drives). Maybe someone could explain how this happens since I'm a noob when it comes to partitioning and installing multiple operating systems

Actually I did install XP first but when I try to install Win7 it wanted to upgrade XP to Win7, so I reformated and installed Win7 first.
I don't have an actual Vista insallation disc. What I do have is HP recovery discs for Vista, but I'm not so sure I want to resort to that just yet. I've never had to use them before and it's my understanding that they restore Vista to it's original factory condition (minus everything I installed) when I bought it a year ago. Alot of data has been put on that drive since then, so I'm really reluctant to go that route just yet. If there are some other alternative solutions I would like to hear them. Thanks again for your input. If anyone has

 

That's nice that you can quote someone elses answer. But does anyone have a solution where I don't loose all my data on my Vista drive? Thanks for your input though.