The issue that you have is that the 845 chipset only supports Intel® Pentium® 4 processors with a 400 and 533MHz FSB in socket 478 (Northwood core). These processors have been discontinued for 7 years. Here are a couple processors that may work on your board http://ark.intel.com/compare/27442,27444,27446,27447
In the end you would be better served by going down to Walmart and buying their cheap desktop then to try to find one of this and think that you are going to get to much of a preformance upgrade out of it.
Intel Enthusiast Team