Ordering ECMLink is really very simple. But to a completely new user, it can be a little confusing if you don't understand the terminology and process already.
ECMLink installs inside your car's computer (ECU). ECMLink supports the 1990-1997 DSM ECUs. You can run ECMLink in a 98-99 DSM, you just have to replace the ECU as described on this page.
The ECU needs to either be an EPROM model ECU or, if it's not, then the ECU will need to be converted from non-EPROM to EPROM in order to run ECMLink. To tell if your ECU is non-EPROM or EPROM, refer to this page. You can get some more detailed information off the EPROM ID page.
There are ordering options on the main product page to allow you to specify whether you need the non-EPROM conversion or not.
ECMLink also supports the early 1992-1995 EVO1-3 ECUs. Luckily for the EVO1-3 guys, all these ECUs are EPROM ECUs.