Can anyone help !

I have up graded from previous pinnicle studio software to studio12 ultimate .
I have also got a new Sony SR11 HD 1080 Cam corder.
I am familer with studio software and made many DVDS
I decided to invest in a new mesh stand alone PC for the new bits the spec is as follows it is used only for the HD editing no internet or anything .

512MB ATi 4870 Graphics accelerator DVI, DirectX 10.1 PCI Express 2 1 75.00 75.00
7.1 High Definition onboard sound card - for 8 Channel Cinema sound 1
NZXT HUSH Silent Brushed Aluminium ATX Midi Tower - Black + 550W PSU 1
Performance Pack - OCZ Vendetta Heat pipe quiet cooling, Performance updates, specialist cabling 1 49.00 49.00
Intel® Core™ 2 Quad Q9650 Quad Core Processor(3.0GHz,12MB Cache,1333MHz) 1 50.00 50.00
Genuine Windows Vista™ Home Premium with Service Pack 1, 64-bit - English 1
ASUS P5N-D Mainboard - Nvidia nForce 750i SLI - Intel Core™ 2 Duo/ Quad/ Extreme - ATX 1 25.00 25.00
Blu-Ray Re-Writer Super Format & BD/CD/CDRW/DVDRW 1 190.00 190.00
Samsung 22x Dual Layer DVD Writer Super Format +R/-R/RW/RAM 1
8192MB 800MHz Dual Channel DDR2 SDRAM - (4 x 2GB) 1 50.00 50.00
1TB (1x 1000GB) Serial ATA 2 Hard Drive with 32MB Buffer 1 25.00 25.00

I belive this to be ample spec to run all this.
However I am having all sorts of problems, the PC is extremly slow and sluggish when editing the HD.
It crashes and is almost un usable.
I have downloaded the latest drivers for the graphics card got the studio 12 update.
Is the problem my end or is the studio 12 really not up for handling the vast info that HD editing does and if so what does that will run on this PC ?
Has anyone else had success with the studio 12 burning HD Blu Ray movies and if so what is your spec ?

Thanks in advance!