OCZ Agility 2 is a good SSD; good value at the moment. BUT i wouldn't buy an SSD right now; the new third generation is coming in a few months and besides introducing faster SSDs (like Sandforce SF-2000 / Intel G3 / Micron C400) that likely means the current second generation SSDs drop in price considerably.
So if you can wait you really should! Buy an SSD in February 2011 instead; either a normal one at reduced cost or a new one with all bells and whistles. The cost is primary factor here!
Regarding AHCI: you first need your controller to switch to AHCI mode; otherwise you're in IDE legacy mode and this will hurt the SSD performance by a good margin. So make sure AHCI is enabled in your BIOS instead. Then you can consider whether to use the default Microsoft AHCI driver or the Intel ones; both support TRIM.