First of all, note that i845GL has no AGP port on the motherboard, so make sure you're happy with having just the onboard video forever. Regular i845 doesn't support PC2700/DDR333 memory. I believe the key differences between the two SiS chipsets is an improved (heh) 3D engine and Hyperthreading support in the 651.
An Asus A7N266-VM with an OEM AthlonXP 1700+ would set you back just over $110 shipped, assuming you have a suitable SocketA heatsink lying around. It would offer better performance and features than any of the solutions you proposed. In CPU-intensive stuff, obviously the AthlonXP has a significant edge. In a gaming situation, the combination of the better CPU and the better onboard video will mop the floor with a Celeron on any of the Intel-compatible onboard video solutions.
The A7N266-VM also comes with superb onboard audio including two types of S/PDIF-outs for Dolby 5.1 AC-3-encoded digtal output, onboard NIC, an AGP slot and a three-year warranty. They're highly reliable, and I would know

since I have 24 at work and two at home. As with any modern system, it would be smart to get reasonably good RAM and power supply (I use Crucial and Antec).
To put it into perspective, I can play UT2003 Demo at 800 x 600 on an AthlonXP 1600+/A7N266-VM system
using the onboard video. If you're just going to type in Word and browse the Internet, then any of your proposed boards should handle it.