OK< Excellent topic.
The genre of space sims is going through something of a fan created reinassence, due to devloted efforts of some very dedicated and talented people and the game industry is finally taking notice and making some moves back into this area, which it turned its back on a little while ago for a while, which is sad because CGI is easily one of the best mediums for this genre.
I agree the Wing Commander series is awesome including some the remarkable aspects of WC III and WC IV which used full motion video and some top ranked actors for the story line, though I agree I and the add ones are remarkable and very very excellent. Chris did a fantastic job on them all.
There is a very strong community in support of the WC seriec, visit the main site at
http://www.wcnews.com/ for all their activites, also for manuals, tech pubs, and mods for all the games, which are blossoming in fan made mods in several game engines as already noted, speifically in both the Freelancer and also the Freespace engines, there are some great mods just now being completed in the Freespace engine that are superb and run flawelessly on the latest platforms XP, and have wonderful graphics. Check on the Freelancer Starlancer community site at
http://www.lancersreactor.com/
for the mods for WC there, and for activity on the Freelancer side of things
The main two leading contenders other than WC as already noted are both
Freelancer/Starlancer by Microsoft, and Freespace, which includes Freespace I with add ons, Freespace II with add ons, and a myriad of remarkable mods as FS was released with full mod tools for the community and that community has risen to the challenge from the very first release of the titles by Origin. As noted, there is a modern fully modern system compatible free version that runs very well on the latest systems and has very high quality graphics.
Other exellent titles in the general space genre are as noted, Tachyon, which can be played on XP in the emulation version available on GameTap, similar to Privateer, ORB and Homeworld (resource and building and fleet action games with beautiful graphics), the X Universe which is a resouce and building game series but with tricky controls that also has a very large community of support, you can also try EVE an mmorpg that has possibly some of the most astounding graphics of any current space sim but in my humble opinion it suffers the same limitations of the X universe, slow grinding and complexities that detract, I would also recomend to you Independece War I and II, I is hard to find and tricky you need to adjust the page file size but it will run on XP, though there are some what steep ship controls to learn for these, but they are fun, I have not tried any of the Star Trek games other than brief reviews for game structure and mechanics, so can't speak on them, and am only now exploring the Star Wars game titles, but in that genre i can recomend Knights of the Old Republic, it is an awesome and remarkable game with much to recomend it, and there are quite a few other titles by LucasArts in the Star Wars universe, and by other companies including both the KOTR titles, I, and II, the Star Wars Battlefront I and II, and Star Wars Empire at War which I have not played yet.
Sooo, I am sorry I can't assure you of finding something similar in all ways to WC I, but there are other interesting games out.
Oh, I did forget, there is indeed a modern version of Privateer with upgraded graphics called Privateer Gemini Gold,
http://privateer.sourceforge.net/
