It depends which version of VS8 SE you have (there are at least two, and possibly more). The major difference that I can remember is the (silly IMHO) decision by Ulead not to include two of the most-used transitions: cross-fade and fade-to-black -- though they were obviously hoping the program's other great features and the lack of these transitions, would entice people to buy the full version. If you have SE Basic, then you may not be able to burn DVDs, though you can still, I think, prepare disc image files (ISO) or video folders (Video_TS) and burn them on third party programs like Nero.
Be aware, though, that a lot of people had trouble with out of sync audio and video in VS8. Not sure how far this might have happened in the SE version, though, since a lot of the problems arose when Ulead started issuing patches in with various version numbers, and depending on the order they were installed, the out of sync problem appeared or did not as the case may be. But apart from general patches applying to all Ulead products, normally you cannot apply product-specific update patches to SE versions.
As for your earlier files, it depends what format they are in. If you just saved them as MSP project files, then you won't be able to open them in VS 8 or any other VS version, for that matter AFAIK. (You can, however, open VS projects in MSP, apparently... Haven't tried that.) Project files are not video files, but merely tell the program what video files are included, where they were when the project was assembled, and what editing has been done to them.
But if they are in a recognised video format (e.g. AVI, or mpeg-1 or 2), then you should be able to open them. From a quality perspective, it would be best if they were DV/AVI. Mpeg-2 is the final format for burning to a DVD,so they would be OK too, depending on their properties and how much editing you intend to do. Mpeg-1 is of poorer quality, being designed to produce VCDs, and at its best is only about as good as decent VHS quality. But if that is all you have, that is all you have!
(Often replies are neither!). I shall check my MS5.2 files in a day or two, when I have set up the relevant HDD into a USB2 driven external box I have just bought. I plan to give VS8SE a try, on a new project, before deciding whether to upgrade, to VS9, or go to the 'equivalent' Adobe or Pinnacle products.