I had no problems installing SEP at all - worked a dream with remote push.
The three machines in question do meet the XP min requirements (just), all the other machines work flawlessly, it's just these older ones that really chug with it (to the level of waiting minutes, not seconds for responses)
The server also runs SMSMSE 7.0
They are non business critical machines running very basic tasks, I have taken the time to refresh the machines and replace network hardware so no other issues are holding them back