I think many people want to use older software on newer PCs.
This contrasts with those who may want to use older versions on older hardware. Often, newer software will not work on those PCs.
Consequently, it would be most helpful to have your web site indicate the minimum requirements. This should include (a) CPU speed, (B) CPU type, such as Pentium I, II, III, IV or Celeron, © Windows version, if applicable.
For instance, Windows 95 lacks certain abilities compared to Windows 98. In some instances this is important, other times it is not. Sometimes the ".NET" component is required.
Since the manufacturer's web site may no longer or may SOON no longer have this information, it would be best to have it available on your web site. As the software gets older, the manufacturer may choose to delete it's information from their web site.