Windows XP Pro 2003 or Vista? What do you suggest?

As some of you know I’m not a IT Pro. I do like to learn new things as an old dog learning new tricks without getting my PCs in hot water.
I’ve learned a few new tricks that have actually benefitted my operation here. My main hardware is 5 years old and custom built (not by me) with Win XP Pro and my new laptop notebook, a Dell has the same operating system.
I will soon need to upgrade my tired overworked main PC and am looking for suggestions and advice as to what I should do.
I use Word, Access, Excel and Power Point software under my Office Pro 2003 package.
Any and all comments welcomed. I do have a thick skin, so no worries about insulting me.