Do you have Windows 98 or Windows 98 Second Edition. I believe Windows 98 SE can run Adobe Reader 6. This can be found on the Adobe ftp site.
The download location for Adobe Reader 6.0 is ftp://ftp.adobe.com/pub/adobe/reader/win/6.x/6.0/enu/AdbeRdr60_enu_full.exe
And where do I stop an auto update from downloading.
By downloading and installing them manually: