Wall Street Journal had an interesting article.
It says:
Excluding labor and shipping, and leaving out the costs of a monitor, keyboard or mouse, the typical desktop PC these days costs the Dells or the H-Ps of the world roughly $437 in parts.
The biggest portion of that — 30%, or $134 — goes to Intel for a Pentium processor. The disk drives, including whatever CD or DVD is installed, cost around $104; the RAM memory is $54; and the remaining hardware items — power supply, case, circuit boards — total $100.
The final 10%, or $45, goes to Microsoft for the Windows operating system.