Hello Linux Community

Last year I lost my Linux box and never got the time to rebuild a new one.  Now it's been age's and I want to start familiarizing myself with linux again and was wondering if anyone knew of a linux distribution that can run as a Virtual machine inside XP AMD64 or upon execution would take over the box until restart.  I vaguely remember something like that.  Otherwise I guess there is always booting from CD-ROM.

Btw:
  Brief background on who I am.  1997 I got my first experience of some flavor of unix on a college minicomputer used for email, web hosting, and teaching c/c++ and learned a lot from it.  2001 I built my first dedicated linux box and turned it into a dual-hosted router/firewall. 
2003 I built a soft Raid 5 Samba File server/apache server/DNS server/ and of course firewalled gateway to the internet.
2005 I moved and the file server of doom was acquired by thieves.  In the near future I want to build another server, but before I do, I want to relearn linux.