It’s hard to be more specific without knowing exactly what you want to access from their computers…programs…files on the PC…network shares…? But, I’ll try and cover a couple of scenarios for you:
In order to run programs, you can right-click the program and select ‘run as’ in order to supply alternate credentials.
Otherwise, you can go to a command prompt and use the ‘runas’ command to access files, network shares, etc. For instance, ‘runas /user:domain\specialuser “cmd” ‘ will prompt for the password of the user you supply in the command, and then run an elevated command prompt. From that command prompt you can use various commands such as ‘net use [letter]: \\mynetworkserver\restrictedshare’ to gain access to restricted parts of your network. Then, you can use the ‘start’ command to open the restricted files.