Solo mining just for luck, realistic?
Check this page: How soon might I expect to generate a block? 

So with the current difficulty  510,929,738, and a 1Ghash/s mining rig (faster than your CPU) you'd do this math:

510929738 * Math.pow(2,32) / Math.pow(10,9) / 60 / 60 / 24 / 365

So to find a block at this difficulty with a 1Ghash mining rig it would take you about 69 years on average.
Good Luck!

PS: Math.pow(2, 32) is simply the JavaScript version of 2^32