I think assembled PCs are as good as the branded ones. Only make sure that the vendor uses genuine and new parts, which of course almost every reputed vendor does. I have 2 PCs at my home, both assembled ones. Since past 5 years they have given me no trouble(no hardware problems, software, of course is a different story!)
Also it’s no good buying only Intel processors. They are too costly. Others like VIA and AMD are quite good and are cheaper than over 2000 Rs. compared to equally powerful Intel ones.
Go for large amount of memory(RAM). It matters more than your processor speed. 800 MHz+256 MB ram would run faster than 1400MHz and 128 MB ram. I suggest 256 MB ram, if u r using the machine for home use and 512 MB ram for office work.
Buy good fast hard disk. Seagate and samsung are good choices. hard disk speed is determined by it’s rotation speed in rpm. 7000 rpm is good enough.
Hope this helps.
Go for assmbled one and save a lot of money.
Best wishes.