If I were in your situation I would spend whatever money I had on a dedicated external soundcard with a properly written ASIO driver. Even if you are only using MIDI you will see benefits. And it's something you are going to need at some point anyway. Decent lower end USB2.0 interfaces can be had for around $100-$150USD.
Unfortunately, the DAW world is not inexpensive
. However, it is amazing what can be done nowadays with just a laptop, Cubase, and a lot of creativity.
That creativity part comes into play big time when working with limited spec gear.
You are either going to have to make adjustments to your workflow or update/upgrade your machine to handle what you are looking to throw at it.