[CentOS] so many problem CENTOS 5.2 with DELL servers????

I have been installed CENTOS 5.2 on several DELL servers and have following problems (even latest patches apply):   1. DELL 2650 can NOT boot under CENTOS 5.2 PAE mode   2. DELL R900 can NOT boot under CENTOS 5.2 PAE mode (inifinite boot loop)   3. DELL R900 with 128 GB RAM can only see 15 GB RAM under CENTOS 5.2 Xen mode   Anyone know why?  IS CENTOS 5.2 certify with DELL server?   Does CENTOS 5.1 have similiar problem or NOT?   Thanks.

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