Yes, as long as:
1. It is not Windows XP 32
2. They are using different urls to connect to the RS 2005 and RS 2008.
Reporting Services 2008 and Reporting Services 2005 (IIS 6 or higher) can coexist in the same machine under most Operating Systems, without causing any conflicts between them. The only exception is Windows XP 32 bits (IIS 5.1). In this last case, you would need to use different ports.
Both, RS 2008 (IIS) and RS 2008 use “url reservations” through HTTP.SYS. IIS uses “Wildcard reservations” and RS 2008 uses “Strong Wildcard reservations” by default.
For this reason, if we had the same url in RS 2008 and in RS 2005 (Virtual directory in IIS) with the same name and port it would be RS 2008 who attend the request.
Reporting Services Support Engineer