DL380 G4 pkgd cluster w/MSA500G2 - upgrade nodes?

[Phil Kingston]

Looking for some advice on a potential upgrade path for my DL380 G4 packaged cluster...
Current setup is:
DL380 G4 packaged cluster - RAID1 onboard system drives, 12GB RAM per node. W2k3 EE, two instances of SQL 2005 EE, cluster in active-active
MSA500G2 with redundant controller/cache upgrade
Shelf is full of 146GB disks in RAID6

I'm seeing that we're hammering the CPU on one node that runs one of our SQL instances. We're happy to buy more horsepower but have (atm) very limited rackspace. We've also got plenty of space left on the MSA. For this reason, I'd rather not buy another packaged cluster simply to spread the load (although that is an option).
What I'd like to do is replace one DL380 G4 in the cluster with a quad-quadcore 32GB RAM DL580 G5. I can quite happily fail over the current SQL node for a weekend, but would be interested in peoples' thoughts on how best to replace one node.
Has anyone done anything similar? I'm guessing the steps would be the same to completely replace one node regardless of it's a hardware upgrade or not.
Any gotchas? or best-practice recommendations? Things that worry me are things like, will the Cluster service be happy having a 'new' identically-named server re-added - should it be unclustered first or what? How will I install a named clustered instance of SQL if an identically-named SQL instance is already running on the other node? Can I even do that? It's no problem to create a new instance name - is that the best approach?
Lots of questions I'm afraid. Grateful for any comments! :-)

[macosta]

Is this MSCS or another clustering package, such as HP's Polyserve Database Utility?

Do you have one big instance, or multiple instances?

[Phil Kingston]

Hi, thanks for taking the time to read through it!
Yep, it is MS Cluster Service and currently has two SQL instances, in active-active during normal operation.