I have had Windows XP and Ubuntu installed on 3 different computers, and I have always found Ubuntu to run faster than XP, even though I had my XP tweaked to use only essential processes on boot up. Forget about Vista. It is way more bloated and resource intensive than XP, especially with those aero glass effects.
You are right though, Ubuntu is getting a bit bloated, and the article I gave a link to in my 1st post in this thread confirms this.
You can disable the compiz and composite effects in Ubuntu if you want. I do. Also, there are many other distros you can try if you don't like Ubuntu. You will always have that choice with linux.
Perhaps you should have a look at Zenwalk. It is a full featured and up to date distro, yet it runs very light and fast. It is quite easy to install and use too.
http://zenwalk.org/

tommcd, I can't believe you when you said that you find ubuntu to run faster than xp. 3 of my friends have said that xp runs faster that ubuntu. So, I just can't believe you.

I just want a fast a light o/s that isn't bloated, that you can install apps with no problems and load them quickly. Zenwalk sounds nice but I don't know much about it to give it my stamp of approval.

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Well, I suppose a lot depends on how you have Ubuntu set up. I don't run compiz, and I have composite disabled. Compiz will slow your performance. When I first installed Ubuntu 3+ years ago, it was quite noticeable that Ubuntu was faster than XP. As I have said, Ubuntu has become more bloated, so perhaps the performance difference is less noticeable now. I would still tend to give Ubuntu the edge though. For one thing, I think linux does a better job allocating memory than Windows XP does.
You should give Zenwalk a try. It is faster than Ubuntum and way faster than XP. You can install it in about 20 minutes too. Read the Zenwalk manual first. There is a link to it on the Zenwalk hoem page.