That P4 costs quite a bit more, runs hotter and isn't any more overclockable than the socket 754 Semprons. That Asus board should be a good board, but again is not inexpensive. Being that the OP specified Sempron I'm guessing that he probably has a budget he has to stay within while still ending up with four systems. Also, work computers... don't necessarily want to overclock them because if you ever get one BSOD that loses work (for whatever reason, virus, adware, etc.) guess who gets the blame if the system is overclocked?
For lilcam, what are the needs of the system? If going with onboard graphics, the SiS 760 GX chipset boards made by Foxconn and Asus would be a good choice. If you are going to use AGP, get the lowest end Epox or Chaintech Nforce3. If you want to go PCI-E, Epox and MSI makes some Nforce4 boards for socket 754. MSI is not that bad a brand. At least they are willing to stand behind their products and accept end user RMA, unlike some other board manufacturers.
If going with a Sempron, I would suggest a "Palermo" core with 256k cache (versus "Palermo" with 128k or "Paris"). Once you get up to the Sempron 3100, you may as well spend the extra $5 for an Athlon 64 2800. They run at the same clock speed and the Athlon 64 has 512k cache. The 3100+ versus 2800+ is because the Sempron is supposedly equivalent to a 3.1GHz Celeron while the Athlon 64 is supposedly equivalent to a 2.8GHz Pentium 4. In both cases, the "slower" CPU is actually faster, got it? Also, may as well get retail boxed CPU because the included HSF is very adequate for getting the job done.
For the rest of the system, get a fast HDD with 7200RPM and 8MB cache of whatever brand. Get only 1 stick of RAM, for instance if you go for 1GB RAM, get a single stick of 1GB, not two 512MB. Consider getting a case that has an air filter and is of "quiet" design. One such case is the CompuCase LX-6A19, available for $40 at Directron.com in two color schemes. That case makes for a sturdy, quiet office computer that doesn't shout "I'm a 14 year old boy gamer" like some of the fuglier cases on the market.
One thought for you is to purchase the CPU and motherboard together from a place like Monarchcomputer.com. I've never purchased from them but they have a good reputation. Why I mention them is that they offer a longer vendor warranty than most places, plus offer extended warranties. The other thing is that they will install the CPU into the motherboard and test it to make sure you don't get a DOA, plus they will update to newest BIOS.