Legacy browser support

I recently redesigned a website for company. I used WordPress 2.8.6 and have since upgraded to 2.9.1. Last night I ran into a problem where a customer of the company called me directly (I have no idea how he got my cell number) and couldn’t login. He was using the standard login that comes with WordPress and would type his username and password but it would just take him to a blank login screen. After a lot of talking with him, I found he was using a 10 year old mac and Internet Explorer 5.1. I know this is not supported anymore so I tried to see if I could get it updated to the newest version so maybe that would help. Unfortunately, I couldn’t get anything installed since he works on OSX 10.3. I then tried just looking for any modern browser but unfortunately, Safari and Firefox doesn’t work that far back. I then tried downloading a legacy version of Safari (1.2.3) which was made for OSX 10.3 but couldn’t get that installed.

Anyways, is there any way I can add a plugin or do something that would allow someone on a really old browser to be able to login?