Firstly, +r may or may not be supported by a network as I believe landon has already pointed out. As he pointed out also, +r is often used to signify that a nickname or channel (or both) is registered, therefore, +R is often used.
I think the original poster needs to make clear about what they class as "unwanted chat". Does that mean non-registered users? Non-voiced users? Swearing? Caps? Flooding? Repeating?
As a recap of what has been pretty much said already:
If you want to stop flooding/repeating/swearing/caps then read
http://helpdesk.zaz.net/documents/protection.php - it has lots of worked protection scripts. They should all work for version 6.14 even though they are written for version 5.91.
To stop non-voiced (+) users speaking use the +m mode. This means that ONLY opped (@) and voiced (+) users may talk.
If you want to stop non-registered users from speaking in the channel then you will need to set a special mode on the channel. Usually this is +M but it might be different (Notice how it's +M
not +m. It is case sensitive). Your best bet is to ask in the #Help channel of the network you use, or check out their website.
If you don't know the website then search
Google.
Finally, if you want to stop people private messaging you then you can either use a query protection script (A 'query' is a private message). You might want to see
this thread, but if you don't know much about scripting you may not understand it. mIRC scripting code goes into your remotes, press
ALT+R when in mIRC. Also type
/help remote scripts for a description. For more query blocking scripts see
www.mircscripts.org and run a search.
Alternatively, there may be a mode on your network which prevents certain users messaging you. Again, you will have to ask in the #Help channel or check out their website.
And just an FYI...
To set a mode on a channel use
/mode #channel +mode - For example,
/mode #mIRC +m will set +m on the channel #mIRC.
To set a mode on yourself use
/mode your-nickname +mode - For example,
/mode adimil +R would set mode +R on your nickname if it is 'adimil'.
Hope this helps.

Regards,