DHCP Fault tolearnce and Load Balancing

The best thing would be to run DHCP in a cluster. It's to expensive to run just DHCP in a single cluster so you could try installing it along other services: file server, Exchange.
Another possibility would be to install DHCP on a virtual machine that runs in a VMware cluster.

PS:  Obvoiusly the trick is not to overlap the ranges... :)

<<Just split the range between multiple servers.  >>>
I might have heard about it, do you have more details on how to set it up?

Have a look at this: http://technet.microsoft.com/en-us/library/cc780311.aspx 

this article also talks about 80/20 rule:
http://www.enterpriseitplanet.com/networking/features/article.php/11315_3327231_3

I wonder why it's not 50/50 rule.

let 's say:

Our DHCP has the following scopes:

192.168.1.1    To      192.168.1.254  
192.168.2.1    To     192.168.2.254
192.168.3.1    To      192.168.3.254
192.168.4.1    To     192.168.4.254

Ho do you split the scopes?

If you need to provide dhcp for different networks, you can't implement it on the same server, you must install dhcp server on every subnet, or if your switch or router provides dhcp for every interface vlan you can use it.
For your example it is the same as I mentioned previously, you can split every range on the two servers on every subnet.
on subnet 192.168.1.1 divide it on the two servers, and like this for all the other subnets, but do not forget each range in its subnet.

let's make it simple
we have this range :192.168.1.1    To      192.168.1.254  
in your suggestion, is to split this range into scopes, and use each scope in a separate server.
I thought that way if one server goes down and your leases are short you run out of IPs.
What I think is a better idea is for instance put 2 scopes in both DHCP servers:
For instance:
DHCP server 1 192.168.1.1    To      192.168.1.126
DHCP server 1 192.168.1.127    To      192.168.1.254  Deactivate this scope

DHCP server 2 192.168.1.1    To      192.168.1.126  Deactivate this scope
DHCP server 2 192.168.1.127    To      192.168.1.254

when one of DHCP servers goes down, all I will need to do is to re-activate the Deactivated scope and both scopes will be serviced by one DHCP server. Then I will take the failed server off line, troubleshoot it, then go back Deactivate one scope of the working DHCp and bring the failed DHCP online.
Would this idea work?

can you do this:
DHCP server1  192.168.1.1    To      192.168.1.126  Activated
exclude from .2 to .20 for static IPs (Printers and servers)
and configure scope options (DG,DNS)
DHCP server1  192.168.1.127    To      192.168.1.254 De-activated
exclude from  .128 to .150 for static IPs (Printers and servers)
and configure scope options (DG,DNS)

DHCP server2  192.168.1.127    To      192.168.1.254 Activated
exclude from 128 to 150 for static IPs (Printers and servers)
and configure scope options (DG,DNS) the same as in DHCP server1

DHCP server2  192.168.1.1    To      192.168.1.126  De-activated
exclude from  2 to 20 for static IPs (Printers and servers)
and configure scope options (DG,DNS) the same as DHCP server1


Now if one of the servers goes down, I will just activate the deactivated scope of the working server.
where could be the issue?

You do not need to make  it complex like that, on my network I configured two servers with dhcp installed and the scope distributed between the two, if one fails clients will take a lease from the other server, but of course if one failed you should have a backup strategy concerning that the failed dhcp server will be back online with its database or not, if not you can extend the existing scope (so there is no need to authorize in active directory),or install dhcp on a newly created server and if you have a copy of the dhcp server backup would be better, if it will come back online and its failure is not catastrophic you should not create another scope since it will conflict the first dhcp server and will add additional problems.

can you show me how you set it up?
with details as I put my settings in details in the example above?

any updates???