Don't move the programs from C!
Just move the data from C to E (although it should already be there, if you have been copying it from C all along) or delete the program stuff from E, if you have been copying it there.
For your backup solution it might be a thought to put the 1TB disk in an external USB caddy and have it separate from the PC.
I would use some of the space on the 1TB disk to create a disk image (e.g. Ghost or similar) of C on a regular basis (keep no more than 2, this week's, last week's, so you aren't over-writing your only copy) to make it relatively painless to recover from a problem. The image will be much less than 320 GB, as it will not include unused blocks and can be compressed.
If you have on-board SATA that supports RAID, and the 320GB disks are SATA, you could create a hardware RAID2 mirror for the system disk and use the 1TB for data - of course you would then have to get another 1TB disk to back that up! It would be the RR solution.
SD
PS - don't use "mirror" when you mean copy: mirror has a specific meaning, i.e. RAID1