Branded PCs are a bad option because they are not optimized in most cases... For eg, you will see a PC with the fastest CPU combined with 128 MB RAM in the branded PCs only... Also, branded CPUs dont give full specs of motherboard, etc, so you dont always know what is under the hood.
AMD Sempron 2800+ with ASUS motherbard (VIA chipset), 40 GB HDD, 256MB RAM, basic keyboard and PS/2 scroll mouse from Logitech, Samsung 15" colour monitor 591s, a CD Writer or Combo Drive or DVD Writer based on your requirement. This will probably be best non-gaming budget computer. The UPS can be a 0.5 kVA UPS (APC, Numeric, Microtek, etc).
Arun