Your version of Microsoft Office (32 or 64 Bit) will determine the version of LEADS you will require.
If you don't know what version of Microsoft Office you have then do the following:
e.g.
Operating System:
Free Hard Drive Space: ~20MB
Microsoft Access in one of the following forms:
(Full Version or Free Runtime in either 32 or 64 bit)
Microsoft Word for Newsletter editing and Outlook for sending emails.