Hi
You do not need a hard disk to find out if it is working ok and what ram, CPU & graphics it has
From Dell web site and serial number you can find out spec & when it was made
Unless you have 2gb of ram no point in using vista , 7 or 8
Some Dells have different specs according to case, ranging from midi tower, desk top & small low profile desk top cases
Are mounting kit for hard disks left behind as many Dells are non standard with easy to remove trays or slides instead of simple 4 screws
Even screws used are often non standard
Often spares inside case
I had to swap 2 hard drives from optiplex gx 520 with a dead sata chip recently
There was also a pata port for DVD drive
I know this is a different motherboard, also check for suitable drivers for sound chips , Ethernet port etc ( I had to use vista drivers for win 7 on this model )
Regards
Mike Barnes