Hi guys
I got back in May 2011 from a year in Samoa working as a Volunteer. I too am a massively keen Surfer and Fisho. I unfortunately only managed one small GT, I targeted them on a handfull of occasions landbased and from boats. Although in amoungst not catching many GT's I managed a heap of other species including Blue Fin trevally, Long Nose Emperor, Coral Trout, Red bass, some massive barracuda, Wahoo, Dog Tooth Tuna, a couple of really nice Job Fish, Mahi Mahi (Masi Masi in Samoan), Rainbow Runners .. the list goes on.
If you are really keen on getting GT's over there Mitch I would suggest you hook up with Asau Bay Resort on the Far North West coast of Savaii, these guys are awesome, they have a great little boat (probably not the best for popping but it'll do the job) and great knowledge of the area. On Upolu you could get in contact with Dive Samoa, they do fishnig charters out around the a small island located between Upolu and Savaii its called Apolima Island, there are some big GT's there .... Dive Samoa is located at Aggie Greys Resort, very close to the International Airport.
If you are looking for waves south coast of Upolu is you best bet, hook up with Offshore Adventures (check their website), A couple of aussie guys (Brent and Clark) own a small charter company and will also do accomodation and meals for a very good price. These guys are a lot cheaper and in my opinion much better value than the bigger surf resorts in Samoa (Salani, Samoana, Aganoa etc etc). Be prepared to loose some skin if it gets big haha.
There are hepas of good landbased spots to chase big blue fin trevally, Tsua Ocean Trench is a must see spot and if the sweel is small a great spot to chuck a lure around, i got busted of there by some big ass Red Bass, Blue Fin and GT's. Again its an awesome spot for a dive if the swell is small.
Hope this helps
Cheers
Anthony