A really noobish question but please bear with me.

[armedRaptor]

I feel really embarrassing asking this but, how do you put gfz grass on a FOF? its been driving me mad.

 

[Kaysakado]

You mean sector borders? There was a special FOF that did that. Too lazy to find it right now.

 

[Shuffle]

The easiest way to do it is to add the GFZGRASS border like you normally would, but not use upper/lower unpegged. Instead, go into DB's 3D mode (which you should be using SRB2 Doom Builder, anyways) and manually adjust the texture offset of the grass. I think you use the up/down arrows.
Make sure to adjust both sides, as the offsets are independent.

 

[armedRaptor]

Ahh, right, thanks shuffle.