Is buying 2nd hand desktop gd?

Puppey SG

Like the ones in http://www.hardwarezone.com.sg/marketplace/list.php?cid=40 ?

And does all monitors work with any other desktops irregardless or different brand etc?

a computer noob here

Raraken SG

My honest-to-god opinion? No. Don't even think about it.

$300 for a P4 2.4GHz? Top up $100 and you can get a very nice modern dual-core.

$500 for a Pentium Dual Core E5200 and 9400GT?

For that cash, get a faster AMD Athlon X2 CPU and higher end GPU + more RAM.

As for Monitors, an Acer monitor will work on a HP machine, A Viewsonic monitor will work on a Gateway PC. As long as you have the cable and connectors required, yes, they will work.

ndmmxiaomayi SG

Given that PCs don't last these days and that prices drop fast, I don't recommend getting a second hand, unless you have a reason to, such as using this PC for test, to break it apart for learning, etc.

All monitors will work with any other desktops as long as you have the relevant cables (unless you tell me you have some super old desktop that has some other kinds of connectors which regular desktops these days don't use)