Mirc has no inbuilt functions to limit download speed (uploads cand be controlled), or even i think the ability to do it script wise. You would be best to look for an external solution, such as a bandwidth limiter, these applications can control the in and out band bandwidth of almost any application. Another option is if your ROUTER (if you have one) may have a QOS section (quality of service), you can control the % of bw made avalaible to each lan Ip, those not requiring any at the time well be passed to the others, this is better than a limitor as it gives u all of it if no one else is doing anything, however the QOS i have always found is one of the harder things in a router to correctly configure.
