I need the Mean time to failure for all these products. If not exact ,
then for a similar product.

Cisco 2691 Multiservice Platform for Core Routers

Cisco Catalyst 6513 switch for Firewall services and aggregation
points for the access layer switches

Cisco Catalyst 3560G for Workgroup switches allowing users to gain
access to the network

Dell PowerEdge 6850 for Web and Database services

Dell PowerEdge 2850 for Application, Email, and File/Print services

Dell PowerEdge 1850 for AD/DNS/DHCP services

Dell Precision 670 for Workstations

Xerox Document Center 440 DC for coping documents
HP LaserJet 4300 tn for Lan Printing

Cisco 2691 Multiservice Platform
Cisco Catalyst 6513 Switch
Cisco 1000BaseT Gigabit Interface Converter (GBIC) (WS-X6416-GBIC)
Cisco Catalyst 3560G-48PS
Cisco PIX 6500 
Cisco PIX Firewall 

Cisco Work 2000 (Network Monitor)
Cisco Work Item (IP Telephony Environment Monitor)

Much of this information may be considered proprietary and simply not available. 

what type of failure(s) are you looking for? That's a broad category. 

JtB()

I'll assume your definition of failure is when you need to reboot or restart
the machine for some reason, and possibly replace/update hardware or software,
to get back to normal operating behaviors. 

The answer is 40k hours for each of the machines mentioned, with 75% confidence
interval.