Can I Limit Apache's Cpu Usage

I have a server running Apache 2 with php 5 as an apache module. There are 2 PHP scripts that get about 500k hits a day. These scripts have to parse data out of a remote webpage and display it on an image. They used to make loads go up to 40-50, but I have added a cache which only updates every 4 hours. This helped a lot, but loads are still around 10 when the script updates, and it slows down the server. Memory usage is fine.
The server is an AMD Athlon 64 2800+ with 1 gb of ram and an 80GB SATA hard drive.

Here's `top` when the cache had just been cleared.

Quote:

PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
28004 named 16 0 121m 11m 3796 S 12.3 1.3 0:00.96 apache2
28003 named 15 0 121m 11m 3740 S 12.0 1.3 0:01.00 apache2
5316 tarball 15 0 43032 29m 2320 S 11.3 3.1 326:08.68 ircd
27998 named 16 0 121m 11m 3808 S 11.3 1.3 0:00.51 apache2
27989 named 15 0 121m 11m 3800 S 10.3 1.3 0:01.14 apache2
28007 named 16 0 121m 11m 3776 R 8.0 1.2 0:00.24 apache2
28008 named 15 0 121m 11m 3776 S 7.0 1.2 0:00.22 apache2
27979 named 16 0 121m 11m 3752 R 6.0 1.3 0:02.06 apache2
27983 named 16 0 121m 11m 3748 R 6.0 1.3 0:01.94 apache2
27985 named 15 0 121m 11m 3748 S 6.0 1.3 0:01.05 apache2
27992 named 16 0 121m 11m 3792 S 5.0 1.3 0:00.33 apache2
27980 named 15 0 121m 11m 3796 R 2.3 1.3 0:03.24 apache2
28009 named 15 0 121m 11m 3796 S 1.7 1.3 0:00.82 apache2
27715 root 15 0 5192 1164 844 R 0.3 0.1 0:00.94 top
27960 named 15 0 121m 11m 3808 S 0.3 1.3 0:01.42 apache2
27984 named 15 0 121m 11m 3804 S 0.3 1.3 0:01.94 apache2
27987 named 15 0 121m 11m 3796 S 0.3 1.3 0:01.04 apache2
28006 named 15 0 121m 10m 3292 S 0.3 1.2 0:00.50 apache2

Idle CPU usage usually goes anywhere from 30%-0%. Is there any way to limit apache from using more than 75% cpu, or any other ways to drop cpu usage?