Yes, continental elites can check-in at upperclass. The security person may try sending you to the longer premium economy line, just stand your ground! I have done pretty much every weekend for the last 2 months!
As for upgrades, getting an operational upgrade on the way out is unlikely. Coming back across the atlantic is a complete different story

(9 out of 10 return flights to london over the last couple of months have been in upper class. One think to note - VS have a policy of NOT upgrading any passenger wearing jeans. I've fallen fould of this a couple of times, and had to hurriedly change into "something more suitable".
There aren't any decent economy seats

If you can, beg and plead for an exit or bulkhead seat (row 40 on their A340s) if you don't want to be eating the person in fronts seat (bulkhead seats are only assigned at check-in from my experiences).Good luck!
Steve
p.s. You won't be allowed to pre-board unless you're a gold elite. Even then, you may need to 'discuss' this with the gate agent
[This message has been edited by steveda (edited 02-26-2002).]