That's an extremely large image to be rendering, especially in this pre-release version of TG2. I'm afraid you are likely to be unable to accomplish any such rendering at this time, although if you had 4+GB of RAM and were running on a 64 bit system (useful for the better memory allocation), then you might have a chance. Improvements in memory management and renderer optimizations should make such large images possible, perhaps using a 'render to disk' function, but those possibilities will not be available for some time.
You should also keep in mind a few things. First of all TG2 has much higher detail possibilities as compared to TG 0.9, and the old "downsampling trick" is no longer necessary to achieve maximum detail. So if you were intending to render at this size then downsample for best quality, you can effectively halve your rendering resolution. If this target of 40x60cm at 300dpi is really what you require, you should also keep in mind that few printers that print at that size actually effectively use a full 300dpi. Most use approximately 150dpi for poster prints of that size, and in general this results in an extremely high quality image, despite the lower resolution than may be expected. Generally speaking such large images are viewed at a much greater distance than an equivalent photo print of even 8.5"x11" (21.6x28cm), so the corresponding dpi can be lower for equivalent percieved quality. I've recently received a poster-sized print created from a 150dpi file and I think most people would be hard-pressed to tell the difference from 300dpi at normal viewing distances.
If you still must have this resolution and want to attempt the full render Ben's advise is your best bet. Unless you're willing to wait for the final TG2 release with which I'm sure you'll have more luck.
- Oshyan