The OP can also give us the model number of the Gateway and we can look up the info for the motherboard that wasy as well which would also tell us the slot type, whether it is AGP or PCI-E.
Antec Nine Hundred, C2Q Q9300 (Currently at stock speeds), Asus Maximus II Formula, OCZ Reaper HPC DDR2 1066 4GB (2x2GB), BFG 9800GTX+, SupremeFX X-Fi, OCZ GameXStream 700W, Seagate 500 GB SATA hard drive, Seagate 750 GB SATA hard drive, Samsung SH-S203N SATA DVDRW, Lite-On LH-20A1L SATA DVDRW, Windows Vista Ultimate 64-bit retail version with SP1