<p>I recently upgraded my oracle client to 10g (10.2.0.1.0).</p>

<p>Now when I try to connect to a legacy 8.0 database, I get</p>

<pre><code>ORA-03134: Connections to this server version are no longer supported.
</code></pre>

<p>Is there any workaround for this problem, or do I have to install two clients on my local machine?</p>

I had to connect a C# code to an Oracle 7 (I know you it's 8...)... the only way I get it was to get the CD to install the Oracle Server and to go in the "Optional Configuration Component" and to use the Oracle73 Ver2.5.
I think you should go check the CD of the Oracle 8 Server and check if an ODBC is still available.