You could probably get the system to run X2 BUT you'll need to fiddle with project much more than you would with an up to spec system. What you should do is build the project up layer by layer using freeze and/or bounce for your softsynths. Example: Get your midi drums together then bounce them. Import the wave file into a new project then put your MIDI bass together (or whatever you want to do next) and bounce to audio and drag it into another new project. Keep doing this until you have enough of a foundation to record your guitar or other live parts over. Record all the live parts you need over top of that (if need be bounce all your backing tracks to a stereo wave so you can jam over top of it each time). Once you have all your live performances done you can increase your buffers so that your computer can handle your mixing and editing. You can crank them WAY up for this because latency doesn't matter in post.
Basically what you are trying to do is keep your synth count down, your live track count down, your active effects down, etc as you record the live parts. Once you have your performance all laid down go back to the first project, raise your buffers, drag all the performances you made into the project so they are editable (eg: if you need to do some midi editing with active synths you will be able to with your buffers cranked up) and then while editing freeze your tracks/synths effects as you go.
Just keep it to low track count audio as much as possible while tracking and you can make an underpowered system work. It's the live synths and effects that start eating up resources. Put the Performance Module into the Sonar Control Bar (right click the Control Bar and select Performance Module until it replaces one of the other modules) and you can keep an eye on how much RAM and CPU you are absorbing.
You may not need to go as all out with the bounce/import to new project procedure as I described but that is one way to free up resource. Again try the track Freeze button as much as possible first to minimize the amount of bounces/imports you need to do.
It is a chaotic way of working but it will minimize resource usage.
There are however much smarter folks than I on here who may be able to provide more refined and elegant ways of approaching this. Also call Cakewalk support to get some tips on system optimization but simple things like disabling startup programs, AVs and windows power management features can keep things from crashing as well.
Good luck.