Its true, most will say to build your own machine. However it doesn't really matter when it comes to ABS. ABS makes some GREAT computers and they are the parent company of Newegg as well. I would know, because I have configured two ABS machines for relatives and they work great. One was a 1.2Ghz AMD Athlon (Thunderbird Core) and the other was a Pentium 4 2.2Ghz (Northwood Core) and they both run great...without a hiccup or anything. They are also known for being very fast, and many magazines love their service and prices. It isn't as easy as we think when it comes to building your own PC. I'd imagine an expert at rebuilding carburetors might think that there is nothing to it, but everyone else will think it is complicated

.
SiS-based? The motherboard in that spec is an ASUS 848P Chipset Motherboard for Intel Socket 478 CPU, Model "P4P800S" -RETAIL. That isn't an SiS motherboard, it even says so in the detailed specs. I think your choice is just fine. I don't know what the purpose of your machine is, but you can rest assured that it will fit the bill for the task. However, I would choose an Athlon 64 system myself. I have dealt with ABS PC many times, as I have said, and they are very good at what they do. Go for a system from them...I assure you that you will not be disappointed.
The P4S800 is an SiS chipset, but the P4P800S is Intel.