Best thing todo is have a search on this forum, as there are plenty of new buils from budget upto very expensive.
something i would recomend.
x58 motherboard eg:Asus
CPU: intel i7-930
12gb DDR 3 Memory 1600mhz
windows 7 64
samsung f3 hd,s
The current CS5 version requires a 64bit computer and OS... Win7 64bit Pro works well
My CS5/AVCHD 1st Impressions http://forums.adobe.com/thread/652694?tstart=0 includes a link to what I built
Do note that AVCHD is CPU intensive, so will edit OK without having a multi-drive RAID setup
Some other HD types are very disk transfer speed intensive, so require a RAID to edit
Go to the http://ppbm5.com/ benchmark page and then to the results page to see what various builds will do
Read Harm on drive setup http://forums.adobe.com/thread/662972?tstart=0
- click the embedded picture in Harm's message to enlarge to reading size
since you mentioned low budget. the AMD 6 cores Phenom work surprisingly well for the price
add a 470GTX and you are good to go. even the 460 would be ok.