As a counterpoint to the posts above, I did a clean install of Vista on my laptop (a reasonably modern model), and it's all working fine. I did attempt an upgrade intially but Vista had a few problems, so a clean install is the way to go I would say.
Microsoft do provide an upgrade advisor utility, which will scan your hardware and software and alert you to any compatibility problems that may occur. It's not perfect though, I would suggest you visit the manufacturers websites of the hardware, and of any software you know you will need to install, to see if they are vista compatible. just do a little research.
Ignore the suggestion of buying a new printer, as it is merely the drivers that would need updating, and not the printer itself.
As to the 'unfinished' claim, that can be subjective. For me Vista loads a lot quicker than XP, it's multimedia capabilities are miles better, it is much more secure out of the box, and the imbedded search facilities are just marvellous. There is an good critique of Vista here:
http://www.winsupersite.com/reviews/winvista.a sp and the recommendation there is to avoid upgrading and do a clean install instead. I did notice bugs after upgrading, but after I did a clean install I've been extremely happy with it. Remember, for every disgruntled Vista owner, there is at least one satisfied customer.
And if you can get your hands on Vista Enterprise then that will be the cheaper option; because Enterprise is not available to the general public, only to corporate customers, which means the only way you would have got a hold of it is for free from a generous person in the IT department! :-)