There is no configuration switch I'm aware of. You can use the following Powershell script to delete logfiles older than 7 Days in C:\WIN2003\system32\LogFiles\SMTPSVC1 and C:\WIN2003\system32\LogFiles\W3SVC1.
dir C:\WIN2003\system32\LogFiles\SMTPSVC1 |? {$_.LastWriteTime -lt (get-date).AddDays(-7)} | del
dir C:\WIN2003\system32\LogFiles\W3SVC1 |? {$_.LastWriteTime -lt (get-date).AddDays(-7)} | del
Then start this as a planned task once every day. Run the command C:\WIN2003\system32\WindowsPowerShell\v1.0\powershell.exe -file C:\Batch\cleanupLogfiles.ps1
in C:\WIN2003\system32\WindowsPowerShell\v1.0
dir. For this example I assuemed your windows is installed in C:\WIN2003
and your script is C:\Batch\cleanupLogfiles.ps1