You should only buy a brand name comp as a very last resort, or if you know literally nothing about computers (like if you don't know what "CD" stands for in "CD ROM")
Otherwise, defintely go for a prebuilt. Just make sure they are good brand components.
Which are good brands?
Mainboards
Gigabyte
Asus
Abit
MSI
Video Cards
Inno3d (local HK company, should have good prices)
Power Color
or any of the recommended mainboard companies
Memory
Memory is usually sold as various brands, but there are the CHIP MAKERS that can differ. Here are some good ones:
Hynix (Hyundai)
Micron (MT)
Samsung
CD or DVD ROM
Sony
Pioneer (DVD)
Philips
Or any of the above recommended Mainboard manufacturers
Power Supply
Thermaltake
Vantec
Enermax
Many non-brand ones are good. Just make sure it is 350W or more, and that it's heavy
Monitors (high end)
Viewsonic
NEC
Sony
Monitors (low end)
Samsung
Proview
Cases
Anything over $350 HKD should be good, but some brands are particularly good:
Cooler Master
Silverstone
Thermaltake
Lian Li
Mice and Keyboards
Logitech (called Logicool sometimes in Asia)
Microsoft
Brands to Avoid There are plenty of brands to avoid, but here are some common ones (refers to mainboards, video cards, etc)
ECS
Asrock
FIC
Hmm I think that about covers it... If you're buying specialized stuff like wireless networking, let me know and I can give some more recommendations 