Yes. You can install SIM 7.1.55 on a 32-bit server. However, you cannot upgrade your SMP 7.0 SP5 32-bit server to SMP 7.1 64-bit, because this is not supported. You must create a new server running Windows Server 2008 R2 64-bit and migrate.
You can find all sorts of documents on the 7.1 migration topic here:
http://www.symantec.com/connect/node/1525181
And the document below explains the process for migrating from SMP 7.0 SP5 (already installed on a 64-bit server) to SMP 7.1, but stresses that reusing the server is not recommended by any means:
http://www.symantec.com/business/support/index?page=content&id=HOWTO32427
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