Ubuntu is no longer a decent Linux distro. Canonical have become arrogant and ignored users needs however well voiced across the many Forums that make reference to Ubuntu. For example Ubuntu 11.10 will not offer the classic GNOME Desktop and it will not include the Synaptic Package Manager despite the fact many users do not want these changes. I used to have much time for Ubuntu starting with Ubuntu 6.10 finishing with the last decent release which was Ubuntu 10.04 LTS
Ubuntu is now losing ground to other distros. such as Fedora and Linux Mint (Ubuntu based)
Fedora often throughout releases includes new software and features a generation before other mainstream distros. Most notable being Fedora 15 featuring GNOME 3 which can only be described as outstanding and a drastic improvement on the Ubuntu Unity Desktop
http://distrowatch.com/table.php?distribution=fedora
It is worth mentioning that the Linux Mint team have tamed Pure Debian to the extent that is almost as easy to install and use as its Standard Ubuntu based Edition. It would seem Linux Mint Debian Edition (LMDE) is the way forward for the distro. but its not quite there yet. The current RC of the latest ISO respin is now available to download and as with Fedora can be run from the LiveDVD
http://blog.linuxmint.com/?p=1807
Overall a Linux based platform can perform most of the tasks equally as well as a proprietary platform using OSS. Linux does have its limitations with some applications and in particular gaming.
If you need to continue using Windows an upgrade to Windows 7 would make sense.
I thoroughly recommend Linux Mint 11. Its easy to install and easy to use plus it comes with much of the software you are likely to need preinstalled.
Linux Mint 11 Download
http://www.linuxmint.com/edition.php?id=81
How To Dual Boot Linux Mint 11 and Windows 7
http://www.linuxbsdos.com/2011/06/11/dual-boot-linux-mint-11-and-windows-7/
Linux Mint 11 Release Notes/Installation Guide/User Guide
http://linuxmint.com/rel_katya.php
Also worth considering is Linux Mint Debian Edition
Linux Mint Debian Edition Download
http://www.linuxmint.com/edition.php?id=88
How To Dual Boot Linux Mint Debian Edition and Windows 7
http://www.linuxbsdos.com/2011/04/23/how-to-dual-boot-linux-mint-debian-edition-and-windows-7/
You download the ISO. image of any of the above distros. then you need to create a Bootable LiveDVD
https://help.ubuntu.com/community/BurningIsoHowto
All can also be run straight from the LiveDVD from Boot without touching your Hard Drive
LUg.