Actually the 3dfx version works just fine, but there is some differences vs the normal versions.
First off, the first patch you had at first does work, the issue i believe is that you forgot dgvoodoo. I am assuming that you do not have a Voodoo card in your system anymore; since that may be the case dgvooodoo is a requirement. You may get the latest beta at
http://dege.freeweb.hu/. Extract the zip into the MechWarrior 2 directory and then run the configurator. You will have to play with the settings abit until the game runs right.
Now, the 16bit subsystem error, that one is abit more tricky.
Usually for me that one goes away on reboot, but if you are on SP3 for some reason it may never go away; least, it has not for me.
There are some suggestions on how to fix a 16bit error at this page
http://vogons.zetafleet.com/viewtopic.php?t=8486 or
http://support.microsoft.com/?kbid=324767
You also meantioned the Mech2XPv3.exe patch; this patch is not compatible with 3dfx.
You only have two choices, either you use the first method you found or use the 2nd method in the video nicknamed kontza's method.
The video suggests that you use the zip to save time, with the 3dfx version you may not be able to do that except for the mw2shell.dll, which you will have no choice but to use; since, kontza's method has a problem with creating mechs. Full details on kontza's method may be found at
http://kontza.googlepages.com/mechwarri ... xppatching
I should warn you ahead of time, the 3dfx version requires alot of cpu power to run; if your system is not highend you may have trouble running it because of all the extra emulation that is going on in the background. You may be better off using the DOS version of MechWarrior 2.
Almost forgot, if you use the first method you found then you need the mw2shell.dll from the zip to use from kontza's method, and you will have to turn some switches off in the shortcut for that method.
/-mechlab is the switch you must turn off, otherwise it will crash upon opening mechlab. This method is the best method. If you choose this method, your game should run correctly, if you do not choose this method you may encounter issues such as jumpjet recharge and missiles exploding as they exit your mech.