As far as I know this could be caused by the different gamma settings PC and Macs have (I think mags have it by 1.8 and Pc have it at 2.2).
So adjust your gamma in your graphic suite so that it matches the PC and you should see how it looks for a PC user.For the image quality try to lower the compression grade.(Use the original grafix for it not the ones allready in jpg!)
Or check how much the filesize is with gif or png (png can even have a gamma setting allowing that it looks the same on all comps but the browser must support it).
*EDIT* forget the shit I wrote above I did a bit research about gamma and seems like the PC have 1.8 and the mac 2.5 the 2.2 value is the avarage of both which is suggested to set so that a image doesn't look too different on one of the machines.
[ 02-06-2002: Message edited by: G.i.A.m. ]
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Wer nicht vom Meister lernt, lernt nie etwas.
Wer nur vom Meister lernt, lernt nie genug.