Through Boot Camp, Parallels Desktop, CrossOver Mac, or similar software. If your employer doesn't provide a copy of Windows, your best starting option is probably to consult the CrossOver Mac compatibility database or run it in the free trial.
Depending of the applications you use, you have to use Boot Camp or a virtual machine to install Windows > https://discussions.apple.com/docs/DOC-3321
If you need Boot Camp, see if you can run a 32 or 64-bit version > http://support.apple.com/kb/HT1846 Then, open Boot Camp Assistant and follow the steps to install Windows on the Mac. If you need help to install it on the computer, see > http://manuals.info.apple.com/en_US/boot_camp_install-setup_10.7.pdf
Boot Camp is a native boot solution and takes complete control of the computer when in use. Other products can be used to run Windows and Mac OS X at the same time(except for CrossOver Mac which translates the instructions directly) and will take up CPU cycles when running, but not when shut down. CrossOver Mac will have less of an impact because it doesn't take up the CPU power needed to run Windows itself.