Do you need xpsp1 yes and no!!
I will not use Vista stayed with Xp pro sp2. Since it's inception there is just too much down time, I use my system a lot for video editing and animations.
Quote from MS.
Before installing SP1, all users running Windows Vista RTM (that is, if you bought your computer with Vista preinstalled) will need to install three updates from Microsoft.
Microsoft's Windows Update will automatically detect and install these updates prior to the release of Windows Vista SP1. Two of these updates increase the success rate for installing Windows Vista SP1; one is necessary only if you have Windows Vista Enterprise or Windows Vista Ultimate installed.
If you uninstalled Vista sp1 that maybe where your problem started.
At this stage what I would do is backup everything and run a repair-re-install using the original Vista setup disc.
or even consider a format and clean install since you have upgraded the hard drive.
What's the brand of your system? If you have an OEM brand lets say HP it will have the recovery discs?
So there is different methods to repair.
Also what are you running Vista home Vista Ultimate etc??
I use these the best illistrated guides on the net but you'll need to select your particular OS then select single page
select your OS from one of the 4 images here
http://www.windowsvista.windowsreinstall.com/laptops and OEM
http://oem.windowsreinstall.com/Main home page
http://www.windowsreinstall.com/
