What do I have to do after installing.

[JJ_the-user]

I installed Ubuntu 8.10 on my pc, along with Windows XP. The first time I runned it, I got some sort of Command Prompt. The place where you type says "grub:". Can anyone help please?

[zwygart]

You probably installed grub not the right way. Does it says any other thing at boot like GRUB boot error?
For the manual of GRUB look at this http://www.gnu.org/software/grub/manual/grub.html
To boot windows try this commands and let me know what happens

rootnoverify (hd0,0)
chainloader +1
makeactive
boot

To boot Ubuntu
type find /vmlinuz
it should write something like (hdX,Y), where X and Y are numbers
then type

root (hdX,Y)
kernel /vmlinuz
initrd /initrd
boot
May you should replace initrd with initramfs. Any way type 'initrd /ini' then press tab. This should complete the command.

[linux_tech]

Try typing in
startx