Hello people. I'm just getting into cutting my teeth in ROR development. Currently all my machines are Windows 7 machines. I know most of the hard core ROR in general use Macs. I definitely won't be able to use a mac. Would you recommending using an ubuntu machine or is a windows machine good enough to get started with ROR Development?
Honestly, without trying to be contentious: no.
You *can* get along getting into Rails using Windows (I started that way with InstantRails), but you will discover occasional things that don't work *quite* how you expect, especially when you get to using lots of third-party plugins/gems. You will probably be better off, going straight into a *nix environment of some description.
The easiest solution is to use a VM (either install your own, or use the out-of-the-box VirtualRails [1] for an all-in-one solution, or the TurnkeyLinux Rails Server [2], either of which you can then customise to your heart's content).
But if you want to make the leap to Ubuntu as a desktop OS it does cut
out the hypervising midle-man 
[1] http://www.virtualrails.org/ [2] Ruby on Rails | TurnKey GNU/Linux
I was developing in windows for a long time but it had many constrains and problems. The best advice is of Michael Pavling, to use a machine similar to the server that you will do the deployment. I can't give up windows so I installed a ubuntu 10.04 server edition in a virtual machine and it is working like a charm. I have a local server on ubuntu with all the advantages, samba to use the files like windows files and I check the site as I would in any other site from my windows machine without any problem.
I use Windows Vista for a lot of my RoR development as it's convenient for me with my current setup even though I run an Ubuntu box as well.
Not everything works in windows, as you might expect, but 95% of it does. This is with a regular ruby install, no instant rails- which is out of date.
You will learn quite a bit using windows. Some of the stuff you learn - how to trouble shoot malfunctioning gems for example - will be invaluable to you later on.
If you have some major computer horsepower you can go the virtual route, but it might be better to dual boot linux.
My advice is to try installing ruby and rails in win 7 first. Take notes and blog about it.