sincec793:
There are lag issues, then there are lag issues. Some are related to your network connection and/or upload/download speeds. Others are related to your hardware. Let's take them in order...
Network: If you're using a wireless connection from your router/residential gateway, try using a wired (Cat-5 ethernet) connection, if possible. A wired connection will almost always be faster and more efficient than a wireless connection is. It might involve stringing/running the wired connection some distance between your router/residential gateway and your computer, and it might require physically moving the computer or the router/gateway closer together.
Hardware: I don't know what your hardware consists of, and performing and posting a dxdiag would be very helpful. If you're not sure how to do this, please PM me and I'll give you a quick tutorial.
However, most reasonably modern computers have a fast enough CPU and sufficient system RAM to run Runes of Magic without incurring local program lag. What usually holds them back is the video subsection. If you're using a notebook computer, there's nothing short of replacing it with a newer and more capable machine that can "fix" it. But if you're using a desktop machine, it's possible to install or upgrade the dedicated video card in it with a more capable unit. Again, having a dxdiag to inspect will be very helpful.