on GX620 DT box (psu) will be possible to install
PNY Technologies nVIDIA Geforce 8400GS Graphics Card (512MB, PCI-Express, Low Profile)
what card may I install in that box?
I need it for video editing, and have more then 1280*1024 resolution
There are no worries about that card what so ever. Your PSU will handle that card and since your box is a mini case the low profile card will fit in just fine and it will do video editing for you at that resolution.
That PC is a perfect desktop for business and other stuff such as your video editing. It migh even handle a few flash games like chess you know the games that come already installed. Hope this has helped and good luck to you.