If your computer tower has another free bay for the DVD writer, an internal one usually works better.
Normally your hard disk is on one IDE channel, and your existing CDROM or DVD ROM is on anther channel. Each IDE channel can take 2 IDE devices. You should add the DVD writer to the same IDE channel as the existing CD DVD ROM.
You need to put the DVD writer into the extra bay, connect the power supply, connect the other end of the IDE cable (which connects the CDROM to the motherboard) to the DVD writer, and set the DVD writer jumper settings to slave.
When all this is done, restart computer, Enter BIOS settings and check that the DVD writer is now detected. Then boot into Windows. Windows should detect it and install the basic driver. Then install DVD writer software.