Gigastudio is not a vsti instrument (with a *.dll extension). It's a progam in itself with an audio driver system propriatery So you can't open it in VEP but you have three solution to manage *.gig file with VEP:
1.The tascam plugin vsti of gigastudio :GVI (Giga virtual Instrument) You can open it in VEP and use your old *.gig file . But two problem this product is discountinued and it is a little difficult to install it under Windows7 but possible (problem to found the e-licence) you must edit the registred data of W7: I did . But GVI is discontinued so windows8 etc...?
2 Gplayer is an alternative .it's a vsti player of *.gig file without to import/conversion :
http://www.soundlib.com/gplayer/
A friend of me use it, but I don't test it.
3.Kontakt import and convert the *.gig
Hope I answer to your question
best regards
Dup