Advantages Of An In-place Upgrade From XP
An in-place upgrade will preserve all your existing settings. For example, in Outlook you'll keep account settings, signatures and offline storage files; in Word, custom.dic and templates; in Excel all your macros. It will also preserve your applications, whether they run under Vista or not. However, if on balance you favour a clean install, then Vista has Microsoft's best ever tool to migrate your settings: Windows Easy Transfer Wizard. This utility is an improved version of XP's User Settings Migration Tool. The Transfer Wizard won't bring over those precious applications, though - you'll have to reinstall those.
Another advantage of an in-place upgrade is that replacing a graphics card or adding memory (if necessary) is much less expensive than buying a new system unit. You'll also save money by buying an upgrade license as opposed to a new license.
Disadvantages Of An In-place Upgrade
With an in-place upgrade from XP to Vista you may be lucky and have everything work perfectly - or you may join the ranks of the disappointed. In the past, whenever I have tried to get an old computer to run a new operating system, I have found one problem after another. It's very annoying to throw good money after bad. At least with Vista you can run the Windows Vista Upgrade Advisor, which is a free download, and will tell you precisely what you need to change on your existing system before it will run a particular edition of Vista. I'll talk more about the Advisor later.
Which Edition Of Vista?
There are five versions of Vista:
Windows Vista Home Basic Windows Vista Home Premium Windows Vista Business Windows Vista Ultimate Windows Vista Enterprise (can only be purchased under Microsoft Software Assurance Enterprise License)