Changing VLAN information

Hi team,

I have inherited a network compromised of 4 Cisco 2950 and 2960 switches, 2 D-links and a netgear.

All switches have been pretty much thrown in and left with their basic configuration for several years. The Cisco's have VLAN 1. We're looking to replace these with HP/Arubas 2530s but with a specified "VLAN 602" for data.

When i replace the existing switches, I'm concerned the users will loose access to the corporate network as the existing servers and PCs will not be on VLAN 602 until every switch is replaced.

Is my thinking correct, or am I going down the wrong line here. If it is correct, how can i minimise the downtime.

I have no access to the current router - this is managed by our MPLS/internet provider.

I have access to all other infrastructure, DHCP/DNS servers etc.

Thanks,

John