Running Ubuntu using a virtual machine will impair performance somewhat. You would have better results installing Ubuntu inside Windows
Installing Ubuntu as a dual-boot with Windows without partitioning
https://help.ubuntu.com/community/Wubi
Download Ubuntu Desktop Edition
http://www.ubuntu.com/desktop/get-ubuntu/download
You download the ISO. image of Ubuntu 10.10 then you need to create a Bootable LiveCD for installation
https://help.ubuntu.com/community/BurningIsoHowto
Ubuntu 10.10 can also be run straight from the LiveCD from Boot without touching your Hard Drive
Ubuntu 10.10 (Maverick Meerkat) User Guide
http://ubuntuguide.org/wiki/Ubuntu:Maverick
I thoroughly recommend Linux Mint 9 LTS and Linux Mint 10 Main Edition which are built upon Ubuntu 10.04 LTS and Ubuntu 10.10 they are easy to install and easy to use plus they come with much of the software you are likely to need preinstalled
Linux Mint has a similar installer called mint4win (mint4win works the same as the Ubuntu Windows installer so the instructions outlined above are almost identical)
Linux Mint 9 LTS Download
http://www.linuxmint.com/edition.php?id=52
Linux Mint 10 Download
http://www.linuxmint.com/edition.php?id=67
Linux Mint 9 LTS User Guide
http://www.linuxmint.com/rel_isadora.php
Linux Mint 10 User Guide
http://linuxmint.com/rel_julia.php
Linux Mint 9 LTS and Linux Mint 10 as with Ubuntu 10.10 can also be run straight from the LiveCD from Boot without touching your Hard Drive
LUg.