I used McAfee ASAP in my former company on 10 computers and it worked a dream. Automatic updating through the server and a status report delivered to my desktop every Monday Morning that told me which machines had not updated that week. (Usually when the owner was on holiday)
This will sort ou everything apart from the spyware but I suggest that MS Antispyware is going to be "Free" according to MS but I`m not sure of the business use implications. All the usual AVG, Spybot, Spywareblaster etc are free for personal use only but they do have paid for options so they may be worth checking out to see if they are suitable for your needs.