I was wondering if you can do your work in something like a medium 640x480 window so you can render quicker as you work and see your product, but then when you're ready to render the final product make it bigger like 800x600. Not sure if those are the same proportions but you know what I mean. Make it bigger in the same proportion.

Set everything up then double click the render button for more sizes than you can shake a stick at.

Sure, you can work it small then render huge. I've been doing that recently.

I always set screen to maximum and then render at 3 times that size. It gives me the ability to fine tune in Photoshop or change the screen size/dpi. Also, I can resize downwards, which of course you can't do the other way round.

You can also do File -> Document Setup...
to get the image size. Just keep the 'Constrain Proportions' checked and that will keep the same height/width ratio when you change sizes.
You might want to do a few spot renders to check textures if you size up too much from your set up size. For pixelation.

cool thanks for your help.

Yup, I have always worked 800x600, then later either increased the document size or rendered to disk.

Also, a lot of times you can work in a lower render quality and then set the quality higher for the final render.  You probably should try some small "plop renders" at the final render quality because a lot of textures change significantly when render quality changes.