Ms office xp

I’ve recently installed a new pc,full OS XP,Office XP (1.7ghz pro.,128mb ram etc..)and it has ran well for about 2 months.
Now the trouble is when i open word or any office document the memory usage in task manager rises till about 20,000 K and above.
I’ve removed all viruses and trojan as well as spyware,done a defrag,scandisk and problem is still around.A word or excel document takes up to 3 mins to open.HELP PLEASE.