Backup exec has a Report feature inbuilt in it and you can even customised reports.

http://www.symantec.com/docs/HOWTO22821

http://www.symantec.com/docs/HOWTO23219

http://www.symantec.com/docs/HOWTO23217

The Device group will give you the required information.  

refer the following blog

https://www-secure.symantec.com/connect/blogs/creating-media-usage-reports

There is no such report that I know of.  This is an often asked question. You would just have to run the job and see how much space is required.  

You could try the daily device utilistation report

Job history will show you how much data backed up per job.

cheats way:

for the job you are wanting to check the size of, you get the start and end backup sets (from teh job log), then in windows explorer go to the folder, order by date time and select the files between the first backup set file name and last file name. This will give you the size of the backup job on disk in lower right hand corner of windows explorer

(this assumes only 1 job running at a  time)

I dont belieive we have Ops centre.  We have Backup Exec for Small Business server, is it included in this version? 

We only ahve one job at a time anyway so checking the size through explorer is a option.  Not a very automated one and should be built into the software but it is a option. 

Only way I can think of woule require some serious scripting

You could parse the job logs to find out amount of source data backed up for each step and divide by the compression ratio to find out how much was written to the backup device, then combine all steps for an over all job usage