It has been shown in most cases here on Anandtech's reviews, and various other sites, that an i815E chipset based board with PC133 SDRAM is either on par or outperforms an i820 chipset based board with PC800 RDRAM.
In most situations, the SDRAM solution, especially for Office applications, will be faster. There are certain programs that RDRAM performs well in, although these are very few.
Given the significant price difference between an i815E/PC133SDRAM system and an i820/RDRAM system, I would go for the cheaper SDRAM solution and put the left over money towards something like more RAM or a faster video card.
I won't say that the i820 with RDRAM sucks, but it's certainly not my first choice.
Although I have mentioned the P3V4X above, which uses the VIA Apollo Pro 133A chipset, its performance can be tuned to have very close performance to an i815E based system.