If you port to VB6, you shouldn't have to make very many changes.
If you port to any version of VB.Net, you will find that the changes are rather extreme. An automated tool will try to do some of the work for you, but depending on how your code was written and what VB5 features you used, you will probably find that you manually need to fix up most of the changes that were made.
The biggest problem is that some of the VB5 features don't have direct equivalents in VB.Net. Do any of your forms use control arrays? You CAN do something at least vaguely similar in VB.Net, but the conversion tool doesn't know about that, so converting them will have to be completely manual.
FYI, Microsoft service packs are available in two forms. The normal update process figures out what patches are needed on your computer, then downloads them and installs them. But there's also an "administrative" version that downloads every change that MIGHT be needed, in one package. That package doesn't automatically install - when the download is complete, you have to manually start it running. The admin version is intended for system administrators, who might have to apply the same patch to dozens / hundreds / thousands of computers on a network - you shouldn't have to download the same data over and over.
The admin service packs won't help you with VB5, of course (unless you find someone that downloaded the VB5 service packs and held on to them). But if you end up going to a new version of Visual Studio (or VB), and you think that it's likely that you'll keep using them more than 6 months or so past the end of Microsoft support, you might want to get in the habit of downloading the admin service packs and archiving them somewhere. It might prevent problems like this in the future.
