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 Accessin one of the following forms:
Full Version or Free Runtime, in either 32 or 64 bit formats.
Microsoft Wordfor Newsletter editing and Outlook for sending emails.