One most common deployment questions that I get is whether it is possible to to have a mix and match of 32bit and 64bit servers in the same server farm. In short the answer is yes, you can.
A little more explanation on this....
The inevitable scenario where you would need a 32bit server is where you have a MOSS farm and you want to crawl Lotus. Since Lotus does not support 64bit C++ API (at the time of publishing this post) it is mandatory to use a 32bit MOSS Server. You can have all WFE (Web Front - End) Server 32 bit and all index servers 64 bit. Essentially, you must have same server level (32bit or 64bit) in all tier of servers. You cannot have 1 WFE in 32bit and the other one 64bit.
Hope this helps.
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