A lot of people have noticed that Redhat Enterprise had some io issues for Pentium 4 processors, this can usually be fixed by updating to the latest kernel and/or putting the following lines into your /etc/rc.d/rc.local file:
echo 100 > /proc/sys/vm/inactive_clean_percent
echo 2 10 20 > /proc/sys/vm/pagecache
This has been said by redhat to be a preformance tweak however it has also saved a lot of people when thier box will randomly lock and thier iowait is at 100%