If he has downloaded Slingplayer and logged into it as the guest, his next move should be to click on 'Connect' in the top-line menu and he should come up with your Slingbox details... failing that I am not sure what to do.
However, one thing that he might try, if he has a windows laptop.. is install Google Chrome and the extension/add-in 'Zenmate'... he will then be able to set Zenmate to the UK and use iPlayer in Chrome! Of course he will not be able to record shows or watch what you have recorded... but it is a near match!
If he's seeing "internet explorer is still running", that usually just means he's trying to restart the internet browser again even though the program is stuck in memory. A reboot of windows and force closing the program usually clears that up or holding down Ctrl,Alt, Del on the keyboard and ending the internet explorer process in task manager will also accomplish the same result.