You're relally getting close to the PSU limit with your current setup, and you would really need a new one for that GTX 295. The card is extremely power-hungry. The nVidia site (http://www.nvidia.com/object/product_geforce_gtx_295_us.html)
states in the specs that the card has a 289W TDP, meaning that you need at least 24A going to the card itself, not counting your other components. Using IDE to PCI-E adapters won't help you.