[wlug] Performance bottle neck?

I am currently importing a lot of data into a Postgres Database. Initially things where quickish, but now it seems to be running very slowly. I put this down to index scans. The machine is a Dual P4 with 2 GB of ram and a Raid array (14 Fibre Channel Harddrives) Top is reporting the disk cache is 1.7 GB and system idle around 70%. The postgres backend is using 10% to 20% of one CPU. I don't know if the bottleneck is the Disk IO or Ram. What would people suggest I can look at to see what is holding up the process?