to tweak the client?
the console client
over any other client.
the client to the start of the partition or hard drive.
your filesystem often.
for dust on your heatsinks.
sure the ambient temperature in the case is cool and not like an oven.
your client at low priority instead of idle.
running the client at normal priority on a dedicated machine.
keep the software up to date.
your flag usage for better workunits.
the use of a ramdrive.
Use linux over windows (stability is key in tweaks).
Makes sure you have a sufficient amount of ram (256mb minimum).
Remove all non required services (NT/2K/XP), go here for help.