Installed Ubuntu on 2nd HD and need to make it dual boot with XP

I have Windows XP installed on my computer and its on a 40GB drive. It was way too full to repartition it to install Ubuntu on the same drive. So I installed Ubuntu on my second 40GB drive but now I have no clue in how to setup dual-booting. I'm very new to Linux and I wouldnt know where to begin please help!

I mean I have played around with it on another PC but I have no experience in setting it up without installing it on the same hard drive as Windows.