|8 hours sounds about right for an i3 encoding HD video in software only.|
Video encoding is very CPU intensive. Extra RAM will do nothing to improve the encoding speed. If you have a second generation i3 (Sandy Bridge), you can use the Quick Sync hardware encoder built right into your processor to encode full HD movies in less than an hour. If you have a first-gen i3, or if you prefer the better output quality of software-only encoding, you should think about upgrading to an i7. An i7 would cut your encode time in half.
Socket 939 | Dual-core Opteron 185 @ 3.2GHz | 4GB | 1.0TB | Win7 x64
GeForce GTX 460 1GB | X-Fi Ti Pro | A8N32-SLI Deluxe | Antec P182