MBR problem

[chown]

Here's my situation:

I have ubuntu on my 320gb hard drive

i HAD fully-functioning mac os x leopard 10.5.3 with graphics, sound, and networking.

while on os x, i formatted my windows partition for a time machine backup partition.

i restart, and this is the beginning of my lovely day

so i put my genuine windows vista cd i "bought" in the disk drive, it goes to the black screen and says "missing operating system". i say to myself "ok, that shouldn't have happened, lets try again."

then i put in my leopard install disk, once again, i get the black screen with "missing operating system"

THEN i go into my brothers room, pull apart his computer, take my hard drive out, put it in his computer, formatted my hard drive, and i thought that would do the trick.

i install ubuntu while the hard drive is in his computer, thought i may as well, because it worked there for some reason.

i also tried changing the boot priority to only boot from cd and nothing else, and when it boots, it goes to the black screen, and "disk boot error, insert system disk and press enter" so i press enter, i get it again, enter, again, etc.

and now all i have, is ubuntu on an 80GB partition

and my computer wont boot from any disk, just the ubuntu partition.

so now im on ubuntu, trying to find a solution, and im not having much luck.

i would really appreciate if someone would tell me how to get leopard back on my computer.