I recommend going with a Pentium III and leaving the Celeron behind. The Celeron system bus runs at 66MHz, while the Pentium III system bus runs at 100MHz to 133MHz. The difference this makes will vary, but at this price you want it anyway. Make sure you get a configuration that includes room to add more RAM later. Systems in this range should come with the Ultra ATA-100 controller for faster disk access.
Upgrades are cheap.
The more video RAM, the less the CPU needs to work. The bigger the monitor, the better the viewing at high resolutions. Before getting a big monitor, make sure you have room on your desk for it. On the other hand, some cable modem providers throw in a free card as part of the installation. The sound card should be good quality, including a subwoofer that adds deep bass sounds.