[AccessD] OT Urgent Win XP Pro

Apologies but I in in a deep hole

I installed the Beta 3 of Office, plus FrontPage 2003 and Viso 2003. System 
started behaving badly and now it will not boot at all.

I need ONE docuemnt off the hard drive. 

I get as far as the Win XP Pro screen then it seems to hand or just simply 
reboot.

ANyone know how  can simply boot to a dos prompt. I know this can be done as I 
have done it before but cant rememebr how.

Martin