v6.0.36 & SQL*Net SPX Problem

I was wondering if anyone has a solution to a problem I'm having with a v6.0.36 NLM database accessed via SQL*Net SPX v1.1.1.0a As you may know, the v3 DOS client tools such as SQL*Loader & SQL*Plus rely upon SQLPME. SQLPME seemed to behave itself relatively well until we upgraded both our LAN token-ring speed from 4-16mbps and our NIC driver (Madge). Now it seems inevitable that at some point while loading SQL*Loader or SQL*Plus on the workstation, the client tool will hang and just lock up. The SQL*Net listener on the server reflects an active connection, but the client is as dead as a doornail. The only way to clear the server connection is to physically turn off the offending PC. After about 30 sec. the SQL*Net listener on the server side finally gets the hint and drops the connection.
I've tried many EMM configs (both EMM386 as well as QEMM v7), tried fiddling with the INT and XMT parameters in my CONFIG.ORA, tried just about everything I can think of on both the PC and Server side (via init.ora) to guarantee a consistent connect, but to no avail. Any ideas? Please e-mail me at the addr below. Thanks. --Brad Gould