It may just be me, but it's not quite clear to me who's computer is coming back asking for quicktime. Is this the first time your friend is using this particular service provider, or has he submitted files before without any problems?
If your friend is burning CD's for the service provider, as David suggests, make sure the proper extensions are being used. Also, make sure that the burned CD is single session/finalized. (Macs don't do packet writing and can not read CDs burned in this manner.)
FWIW- I exchange files on a daily basis between Windows and Macs and have no issues whatsoever...jpeg, psd, Word, etc...