Although the Vista upgrade has been designed to install over earlier incarnations of Windows, I don't recommend that Vista is installed in this way - I advise that you perform a clean install which, with the upgrade version, actually means installing twice, once WITHOUT the product key (make sure you select the correct version when prompted) and then an upgrade installation on top of itself WITH the product key. See the Tutorial for full details. Problems can occur when upgrading to Vista from earlier versions of Windows if you don't follow this method. These are usually driver and other configuration problems. Even if you have no problems initially, that doesn't mean to say that you won't have any in the future because of this method of installation - as you have found out when trying to install SP1. Unfortunately, you have provided no hardware details so we cannot help you if the problem is a hardware matter. As well as that, you have not specified whether you are running the 32-bit or 64-bit edition of Vista (I suspect 32-bit, since you have upgraded from Win2000). I provide links to the standalone versions of SP1, both 32 and 64-bit. As a bonus, I also provide a link to the Office2007 SP1 download. You can place both the Office2007 SP1 and Vista SP1 on a single disk for convenience. For the 32-bit version of Vista SP1 you can use a standard 700MB CD, but for the 64-bit version you will need a DVD. Clean Install From Upgrade Vista Download details: Windows Vista Service Pack 1 Five Language Standalone (KB936330) Download details: Windows Vista Service Pack 1 Five Language Standalone for x64-based Systems (KB936330) Download details: The 2007 Microsoft Office Suite Service Pack 1 (SP1)
After installing Vista according to the above Tutorial, immediately install SP1. This is really the best way to do it because by doing it this way you are minimising any potential problems caused by erroneous registry entries, which, on a clean installation, should be non-existant. This is actually the closest that we can get to installing SP1 at the same time as Vista, bar, of course, using the versions of Vista now available with SP1 slip-streamed in. Should you wish to create a slip-streamed version of Vista with SP1 built in, the link to the appropriate Tutorial is available from the Tutorial link that I provided above.
When you have successfully installed SP1, you can install your anti-malware programs, connect to the Internet and use your PC as before.