There is very little chance the Service Tags on the machines are wrong.  You can confirm them in the BIOS if necessary.  I can't give the same assurance for the Support Site to return the correct information, however, all four that you sent me came up as Optiplex 745's.   [URL] Small Businesses, System Configuration (menu on the left), Enter Your Service Tag, then System Configuration tab gives me the correct information.
Our community partnership have inherited 75 Dell Optoplex GTX620 pc's donated by a local school.  The HDDs for obvious reasons have been wiped.  We were not given any software.  55 of the PCs do not have any COA, and several have part of the coa torn off. WE have installed/activated XP SP3 on those with COAs fine. Does anyone have any suggestions how we can install and activate XP on the other 55 PCs that don't have a COA; looking at where the COA normally is they look as though they never had the COA stuck on originally. Thanks for any advice.
No COA stickers, wiped hdd, no Dell branded XP OS CD