If both systems have a Windows Vista Home Premium COA it will make no difference. A single Dell Windows Vista Home Premium Reinstallation DVD can be used on all Dells that came with Windows Vista Home Premium.
The systems are are about the same age and should have the same OS installed unless you customised them.
As you are donating your PC you are best to follow my Windows Reinstallation Guide/A Clean Install of Windows Vista:
http://philipyip.wordpress.com/dell-community-forums/
The initial steps will explain the COA and what media to use.
You should carry out the optional Step 7a and completely wipe all data from the machine (as you never know what can happen to a donated machine).
