messed up windows boot..newby

[bullardjuk]

OK so I would like to try Linux. Got a ubuntu feisty fawn 7.04. Windows XP installed on hard disc. So I try to install linux on external hard disc. External disc also used with other compters and often switched off.
Grub has loaded itself, without asking, onto external disc.

Now after Bios, message..'Error cant find Grub'. (Not surprising !)

If External disc is on all is ok and have choice windows or linux.

I have Partition Magic 8 and Boot Magic but they do not seem to be much good now.

How, in very very simple terms, can I put Grub onto the windows disc?? and make it work from there?
--
Dave