United miles don't expire if you have an activity on your account in 36 months. So the best thing would be to generate an activity and build these miles to a level where you can get some use of them. A transfer from Diners Club to your United account will generate activity extending the life of the miles for another 36 months. Look at the United forum or www.mileageworkshop.com for tips on how to get United miles.

5,000 United miles can be transferred to 10,000 Hilton points.

10,000 United miles can be transferred to 10,000 Diners Club reward points. This will devalue these miles (so you'll lose 50% in the conversion), but if you subsequently use a Diners double conversion promotion to British Airways, you will get 10,000 British Airways miles.