I got the same situation...
I don't have the $ to buy a muscle g5, so I just purchased some ram and a new hardrive to max up my macbookpro.... 6gbRAM and 500gb harddrive @ 72000rpm... form
https://eshop.macsales.com/
Quantity: 1 OWC5300DDR2S6GP, $184.99 each
6.0GB (2GB + 4GB Module Set) Upgrade kit for MacBook(Late 2007/Early 2008, MacBook Pro(Mid/Late 2007, Early 2008), and iMac (Late 2007) systems with Core 2 Duo Santa Rosa or Penryn processor. Lifetime Warranty.
Quantity: 1 SEAST9500420AS, $134.99 each
500GB 2.5" Seagate Momentus 7200.4 7200RPM **SATA** Notebook drive with 16MB Cache - New with 3 Year Seagate Warranty.
I already have a (G-Tech G-DRIVE Q - Hard drive - 1 TB - external - FireWire / FireWire 800 / Hi-Speed USB / eSATA - 7200 rpm - titanium) , and that's where I'll be working and saving al my fcp7 files...I hope it'll be enough since I'm just working with about 30 min of HD video... Can anyone confirm....