If you mean you can't access LAN in Tiberian Sun because you're using Vista, this issue was fixed in version 1.08 of DTA by applying Scorpio9a's Tiberian Sun and Red Alert 2 LAN Patch.
IPX doesn't work with Vista, so what the patch does is making Tiberian Sun use UDP instead of IPX. To also fix this for Tiberian Sun, simply go to the link above, download the patch and place wsock32.dll in your Tiberian Sun dir. Take in mind all players will need to have this patch (even people without vista) for this to work.

THX!!

I'm having trouble playing over Hamachi on Windows 7 with another Windows 7 user who just downloaded the game, has anybody got a suggestion on how to make this work properly?

I've only tried getting into Tiberian Sun's LAN on Windows 7 once (both with and without Hamachi installed), but didn't manage to get it to work. I personally don't have Windows 7 installed, so I'm not sure whether this is a Windows 7 related issue and whether there's any way to get around it.

http://www.moddb.com/games/cc-red-alert-2/downloads/ra2yr-lan-fix-xp-vis...
I was looking around for something and came across this.
This one is said to work with Win7 32 and 64, haven't had an opportunity to test this though.

Tiberian Sun already makes use of the wsock32.dll file; it's just been renamed to UDP_DTA.dll. So unless the one you linked to is a new or modified version of the wsock32.dll file that used to be on understorm.net, DTA already uses it by default.

Well, seems to work for me without modification in that case, I'm on Win 7 64, and I haven't had the problem I had with the other one.

The one you linked to also isn't going to work with DTA, because that file actually checks for "Game.exe", while DTA uses DTA.exe. So if you can get on LAN in Windows 7, it means that the included dll file works just fine

I've got LAN (both real LAN and Hamachi) to work with Windows 7 when playing with XP users, but every time I've tried playing with two PCs running Vista/Windows 7, the Vista/Windows 7 machines can't see each other but they can see the PCs running XP.

(and the computers running XP see everyone).

That's kind of weird... My best guess is that compatibility mode might help (to some extend).

maybe you should try giving hamachi a higher network priority than your LAN has. fixes issues with many games.

For me it already has a higher priority by default, but for those for which it doesn't, it might indeed help.

For me and my friends (who are all running either Vista or Windows 7) Hamachi also has higher priority, so it doesn't help.

I could try compatibility mode though if we try it again sometime.

- make sure you have version 1015 or less (i use 1014)
- try aliases.txt
- try forcebindIP as last resort (only way to make starcraft work for example)

and if AAAALLLL of this fails... try google

I use the newest version of Hamachi, it has always worked perfectly with all games, even with TS and DTA, since the problem which I described happens not only with Hamachi networks but also in a real LAN.

ForcebindIP sounds interesting though.