A Palermo 3000+ (S754) is rated @ 1.8GHz and all K8s 1.8G and above support C'n'Q (I know that only the 2600+ and 2800+ have C'n'Q disabled).
Power consumption is 65W but you will probably be able to undervolt it to a good 1.30-1.25V and make the TDP drop to 45-50W on full load, so overall I think it will be decently low power.
2003 server has low system requirements (lower than XP), so it won't be a problem to handle it; just consider that it won't be far from an A64 3000+.
I don't think it does. I looked at that for the same reason as you, and in the end went for an Athlon 3000+ because of the CnQ. There was very little difference in price (about 5 pounds I think) and the Athlon is quicker at the top end when needed.
Keep in mind that idle, with or without C'n'Q, the CPU will consume more or less the same energy; I remember when I had the A64 3000+ (1.8G), the difference between idle temperatures with and without C'n'Q (1.0G and 1.8G) most often did not get larget than 1°C.
IMO, you can even use a dirt cheap 2600+ because the most important thing in lowering hat dissipation and power consumption is undervolting, not C'n'Q. I used to run my 3000+ overclocked to 2.0G but undervolted between 1.25 and 1.20V and that brought the load temps down a good 5-8° while on the other hand, C'n'Q does do any considerable job on a single core, especially at those frequencies. You should seek undervolting moch more than C'n'Q.
not sure about the sempron 3000, wifes old 2800 did not support c&q. curretly im using my old a64 3000 mobile (s754) for my server. it does quite well, but either way, undervolting the the biggest key here.
An 'old' Sempron 2800+ might also refer ro a socket A Sempron 2800+; ALL K8 (S754, 939 and AM2) Athlons and semprons do support Cool'n'Quiet. However, as I stated above, judging by my previous experience with the Athlon 3000+, undervolting is a much powerful method than C'n'Q for lowering power consumption, especially at these low frequencies. Just take a look at the PCU calculator and play with the OC voltage lowering it and keeping the OC frequency the same as stock: http://www.extreme.outervision.com/PSUEngine
On 1.25V, the Palermo Sempron 3000+ consumes only 49W. If I were Apache_lives, I'd nail the 3000+ @ 1.4GHz with CrystalCPUID (by making a scheduled task that runs the 7X multi on windows startup and setting power management scheme to 'Home/Office PC') and that would be enough to make it run on only 1.20V; that gives a miserable 35W.
my wife old sempron 2800 was s754, infact it was the sempron 64 2800. i tried everything to get c&q to wok to no avail. although the box did say it had it. i know it wasnt the board as the board was the same as the one i was running a a64 mobile 3000 in.
Well as I said at the beginning, only K8s of 1.8GHz and above have C'n'Q enabled (stupidly wrote ALL in the previous post ), because for 1.6GHz and below, it does not really make any difference. On my Athlon64 3000+, the difference between idling with or withour C'n'Q was at most 1°C; which also means a very small consumption difference. That's the reason why they disable it on 1.6GHz semprons.