Would like advise on upgrading memory to my Dell XPS T600r.  I keep up with security upgrades and system maintenance.  It's almost 5 years old and reliable, but intermittently slowing when surfing the net ... sometimes badly and I need to restart the computer.  The computer has the original confirguration from Dell, 128K memory.  I would like to get another 6 months to a year with the computer before I buy a new one.  Is it worth the $75 to $100 to upgrade, or would you advise a new computer?  Many thanks!