This has nothing to do with your Outlook Express, unless your friends are still sending directly to Hotmail because your Outlook Express setup still has the Hotmail account as return email address mentioned, and this is only possible in case they reply to any mail you sent them in the first place.
I don't know Virgin Internet, is it possible that you have the option there to forward your mail to some other account, in your case Hotmail?
Go to your Virgin account and double check the settings there.
You can see these replies also if you simply send an email directly to your Virgin account. If you do not see any reply coming in after some time, than also your friends do not receive them.