1 firewall (the one in XP is not good enough, Windows Firewall for vista & and 8 is OK)
1 Antivirus (more than one will clash with each other and possibly really slow your machine
As much antispyware as you want - One real time scanner and one as a backup to scan weekly to make sure your first is good enough (Some antivirus programs include antispyware scanners.)
On XP I use Sygate firewall - Avast antivirus/antispyware realtime scanners, Spywareblaster as a blocker, Malwarebytes and SAS as the backup checker for Avast not had a problem for years with this setup.
I use MSE on another XP backup machine but an not that happy with it.