Under most conditions, this is not normal, although there are some possible reasons why this could happen.

1) Windows 9x machines don't behave well with a lot of targets. The standard ICMP mechanism in Windows 9x takes a lot of CPU for each outstanding thread. Windows NT based systems are recommended for a lot of targets.
2) Really fast ping intervals, coupled with sorted target lists means that the target list changes a lot, which can cause excessive CPU use. This is particularly a problem where the sort order of the target list changes a lot (ie: you're sorting by latency or packet loss).

If you let us know a bit about your configuration, we'll be happy to help you get this solved.

- Pete