Data entry / cell format problem?

I transferred files from my old laptop (XP) to a new one (Vista). Today I opened a spreadsheet that I use to record timings of work tasks, entering a start time in one column, the end time in the next column, and then typing (not calculating) the difference in a third column:
Example: 21.30 21.40 10
I can enter the start and end time without any problem but each time I type in the difference (in minutes) it is not displayed as an integer - instead 10 minutes appears as 0 or 0.1 if I apply decimals. In each new spreadsheet any integer I enter fails to appear as integer and again is showing up as 0.x.

It looks as if this is a general setting but I can't work out what it is and how I change it back? Very grateful if you could help. Many thanks.

right click on cell with difference and format,, choose custom and hh:mm

this should do the trick if understood your problem correctly.

why not do simple subtraction calculation,, it should automatically sort the formatting for you?