Ubuntu
The Ubintu/Linux boot menu after using the same installation for many times would look incredibly messy with entries of older Linux kernels remaining active.
Interestingly, a large number of Linux distributions are available, may be cause it comes free of cost and there are a lot of unique reasons to like them.
I always believed that the concept of Wine somewhat defeats the purpose of a Linux as an open source operating system.
What could be the best use of your old computer? Before it is rendered completely dysfunctional, you can turn it into a file server, game server, arcade console or anything for your use.
Following the grand releases of Snow leopard and Windows 7 the latest Linux distribution - Ubuntu 9.10, or Karmic Koala made its debut recently.