Accounting to reports, ecs is the number one mb manufacturer in terms of number, overtake ASUS end of last year/ begin of this year.
Its main business is OEM market, much of the boards are not overlock friendly.
Coppershim is for proctection against damage on your Athlon CPU. Some ppl force too hard when installing the heat sink and damage the CPU. So its up to you if you like to buy this "insurance" or not.(be sure to choose the one that fit, i think XP may use a little different shape)
heat transfer? I don't know what you are talking about....sorry. may be you are saying the coppershim help heat transfer? i do not think so. Or you are talking about the heat transfer between CPU to the heat sink??