Which OS do you use? If you are using Vista then You can try to disable many visual features in Vista, in order to take a lot of load off of your CPU and drastically increase speed.

1. Disable the fancy Vista Interface and return to the "Classic" windows interface. To do so, go to the Control Panel and hit "Classic View" on the left side, this will bring up a lot more icons which are easier to navigate. Then click on the "Perfomance Rating and Tools" button. This will bring up a new window with a lot of features to help improve the perfomance of Vista. On the left side click on "Advanced Tools" and go to "Adjust the appearance and perfomance of Windows" near the bottom. Under the "Visual Effects" tab click on "Adjust for best perfomance".
2. In the same window under the "Advanced" tab you can choose to change your page file or virtual memory size. This is what windows uses to store application data when there is not enough physical memory on the computer(RAM). It allocated a certain amount of space on the hard drive, and by increasing this value by a couple hundred it can cut down on the amount of time windows spends resizing this file.
3. Reverting to the windows "Classic" theme can also cutback on CPU and GPU load to help improve perfomance by making the graphics less consuming. To do this right click on the desktop and go to "Personalize" you can then click on "Theme" and change it to "Windows Classic".
4. You can also use the many tools in the Control Panel--> Perfomance Rating and Tools to look for suggestions from Vista as to why your computer is running slow. Check under the "Perfomance Issues" area on the "Perfomance Rating and Tools" main menu.
   I hope it will help

I think Poplar would be a good choice for the frames. It is tight pored and would take the paint very well. I recently made two hallway benches out of poplar and it is very easy to work with. I made the cases out of the poplar on these two pieces also because they were stained instead of painted but that can get a little pricy. If your cases are not going to be exposed, I would opt to use birch plywood probably. I personally don't like working with MDF. Clear select pine would also probably work well but has splitting tendencies sometimes.

However, I recently made some raised panels for a couple of doors and frames for my brother to put in his new retirement cottage loft, and these worked really well. He was going to finish them natural instead of painting them though.