playback engine set up issues... need help!

[tingly]

i'm getting a lot of errors saying "A CPU overload error occured. increase H/W Buffer Size".

but i'll get these errors even when i just opened a new session and i'm tracking my first couple tracks.
i'm running on a G5 power PC mac dual 2.0, 1 gig of ram, and 150 gigs of free HD space.
i'm running an A/D converter into the S/PDIF input of the mbox2.

i've tried running the H/W Buffer Size at every configuration and i still get these errors.
i never had these problems when i was running ver 6.7 and going in through the regular 1/4" inputs.

i'm also have some latency issues too.

can someone please tell me how to fix this, or how i should have my Playback Engine set up?

H/W Buffer Size:?
RTAS Processors:?
CPU Usage Limit:?
DAE Playback Buffer:?

i read the manual but it's too technical for me to make sense of it.

please and thank you!!!

[sky88dd]

Are you recording to your system drive?

[tingly]

no i'm recording to my lacie firewire external drive.
and inserts i'm using are just the basic protools EQ and compression effects nothing too fancy.