Slow system

I have a PIII 450Mhz, 256 Mb plenty of HDD space, use McaFee Virus scan.When I send a job to print the whole system slows or stops untill the job has passed to the printer,this also happens on applications/ faxing etc.I have completed all maintenaceschedules defrag, removing temp/ history files etc have increased the ram to 256 with a little improvement. I feel it is a memory conflict but do not know how to correct. Is it advisable to get system analysis software or any other help welcome.