Maybe it's just a coincidence that they look similar in nomenclature.
The last AMD processor I had was a 486 and my current PC is using an Intel PIII and chipset, but my PC at this moment has two of the ATL.DLL modules loaded while I write. One in the winnt directory [v2.00.7016 - 18k 1998], and one in the system32 directory[v3.00.8449 - 56K 1999]. Since if your really don't know what they do, I would just ignore them. Both of my atl.dll files look like they are older than most other made for 2000 drivers although the dlls vary significantly in version prefix (probably for x86 compatibility from win32 to win16 and DOS). Most drivers made for 2000 (not dll's) usually start with 5.xx, not other prefixes below 5. Maybe the dll is for the Athlon, but I wonder.
I could be just ignorant, but I don't think ATL.dll has anything to do with the Athlon but more likely to relate to ATL's. ATL's (Automatic Tape Libraries or Loaders) which can be managed through the Storage manager (under Computer Manager, near Logical Disk Manager). This is where you modify and setup your tape libraries for Tape Loaders, whether manual or automatic. On the other hand, the amd751.sys driver file is an AMD AGP filter driver, has a version of 5.x and does not run as a driver on my system, cause I don't have and AMD CPU.