unable to delete the "NSR peer information" entry for storage node

Are you trying to remove NSR peer information via nsradmin? Try to add administrator so that from backup server cmd you do nsraddadmin -u administrator and retry operation again.

In 7.3 there is no nwadmin anymore (unless used from client with pre 7.3 version - but I would recommend to use it only for read only operations - not edit ones).

No, it's java based web application so you need browser and older 1.4 java for it. On NMC server you will have SQLAnywhere database where NMC will keep its own repository for data handled. It's bit different than now - NMC is more than nwadmin was. nwadmin was GUI interfaces to NetWorker database and configuration. NMC is that, but also it seems to be designed to enhance security access to that data and do some basic reporting (which is not 100% accurate from what I have seen so far).

What GUI interface do they use now? I have become very attached to it.

In 7.3 EMC replaced nwadmin with NMC. Some people like it, some don't. If you are attached to nwadmin you probably won't in the start. You can still use nsradmin or even nsrwatch for quick check, but NMC is now new GUI.

Or add the client to the adminstrators list on the server, I use the GUI nwadmin so it is real simple to do.

I will have to look up more on this but does it run in xwindows on the server?

You can use command line to delete a "peer host". Try the following from you NetWorker server:

nsradmin -s host_name -p nsrexec -c "type:NSR peer information"