Which hard drive config is the best for an existing system?

Hy there,

We have this system:

DELL PRECISION T3500 64 BITS CPU

INTEL XEON W3520 2.67GHZ  266 MHZ 4 CORE - 12 GB RAM

NVIDIA GEFORCE GTS450

MATROX RTX2 - 5.1.2.8

PREMIERE PRO CS5 (5.02)

WINDOWS 7 PRO

SYSTEM HD 500 MB

With this HD config:

B: EXPORT (partioned with C:) - 7200 rpm (250GB) sata - to this HD we export all final media

C: SYSTEM (partioned with B:) - 7200 rpm (250GB) sata

D:AV - PROJECTS + SCRATCH (MEDIA PREVIEWS) - 1 TB sata - here are the captured audio/video, Premiere projects, previews, mxtemp, etc.

Now we will install another 3TB 7200 rpm Barracuda HD, so we need to reorganize everithing in way to eliminate the partition (?) and redirect  everithing for a better result.

So which config we must to use with ?

Thanking beforehand

ALBERTO