A single CentOS 5.2 x86_64 machine here is overloading our NetApp filer with excessive NFS getattr, lookup and access operations.
There was a kernel update in the 5.2/5.3 time frame that fixed a NFS client bug regarding lookups, what kernel are you running?
2.6.18-92.1.22.el5. I can test all newer kernels if necessary.
Please update you centos installation. It will probably fix your NFS issues and your current system contains serious security problems. "yum update".
/jens