You may word this as you wish, but what this is saying is:
la admisión de un pago parcial (que de hecho constituye un incumplimiento, i.e., "such default") no constituye por parte del Arrendador una renuncia de su derecho a exigir el cumplimiento futuro de los términos del contrato

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Note added at 12 hrs (2007-03-18 09:53:22 GMT)
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For info:
non-waiver clauses of this type are fairly standard in most contracts. Here is a definition:

Non-Waiver
The purpose of non-waiver language is to protect a party who excuses the other party's non-compliance with contract terms, and to prevent the parties' course of conduct under the contract from resulting in the loss of enforceability of the actual terms of the contract:

The failure by one party to require performance of any provision shall not affect that party's right to require performance at any time thereafter, nor shall a waiver of any breach or default of this Contract constitute a waiver of any subsequent breach or default or a waiver of the provision itself.

For example, if a contract requires monthly payments but the party owing payments only pays every other month, in the absence of a non-waiver clause, after a year of acceptance of the late payments a court would be likely to hold that the bimonthly payments do not constitute a breach of the contract. With a non-waiver clause, the party to whom the payments are due would typically be able to enforce the monthly payment provision, despite the course of conduct which was inconsistent with the contract language.

http://www.expertlaw.com/library/business/contract_clauses.h...