Actually, if you have that many applications running, I'd opt for a second System taking care of the SERVER work. Get a 600Mhz Duron and an Abit KT7, run it a 1 Ghz (mine is doing 1.050GHz smoothly) and invest in extra memory.
256Megs is not a lot for the multi-tasking LOAD your suggesting.
Equipe both your systems with at least 512MB. I have been building systems proffesionally for quite a few years now and there are only very few advantages to a DUAL System:
1. System seems to be more stable (especially running NT4)
2. When rendering (MAX3.1) you'll get up to 80% performance increase (but have a look at TOM's P4 benchmarks and you'll see that a DUAL PIII 1GHz won't come close to a single Athlon 1.2GHz)
3. They are more expensive than a single but usally less expensive than two sytems, although that might not be true with current Intel Platforms. If you were to go for a DUAL PIII based on the i840 you would have to buy RDRAM (getting all thoses *benefits*) and you would certainly spent more money than you would b e spending on a second ATHLON/Duron. I wouldn't recommend any of the VIA based Intel DUAL Systems because the Memory Performance of the 694X is WEAK.
A major drawback of any dual system is the excessive amount of heat produced. You will need a large tower, a lot of fans (and mak'em BIG) and some major powersupply (don't go below 300 Watts)
If you REALLY want a Dual, try to get hold of the TEKRAM P6B40D-A5, overclock the BX to 133MHz and get some nice PIII EBs (2x933Mhz) and last but not least HIGH Quality Mermory (Micron or Infineon PC133 CL2).
I would opt for the 2x Athlon/Duron solution and don't bee annoyed by the NOISE.