Is there a way to download games while playing MMOs without causing lag? Is there a way to set the modem to download at maybe 30 percent and leave the remaing 70 percent for the MMO game? Everytime i try to download a game during my MMO session, i get very bad lag.

If you're talking about GOG, you can limit the download speed in the downloader settings

You mean downloading via GOG Downloader or browser? For GOG Downloader you can set up Download speed limit in Settings and for browser you can use some add-on.

edit: ninja'd :D