network load balancing (NLB) doesn't throttle the connection.
it spreads incomming requests over 2 or more servers.
the connection speed and bandwidth is still just the same when you are connecting to the internet. -as if you have 2 non load balanced machines.
the point of NLB is that you spread incomming connections over more than one server so that the servers are not maxed out. it has little to do with the speed of the connection externally. (i.e you spread 500 concurrent connection over 2 servers so 1 server deals with ~250 and the other server deals with ~250 rather than one server dealing with all 500, which might make it poo it's pants).
A form of network load balancing called NIC teaming or bonding can be used to give 2 adapters in the same server a single address, in this case the bandwidth to the server is actually roughly doubled since the bandwidth of both cards is added together.
(this is easiest on internal connections like using 2 NICS on a server plugged into the same switch, though you can bond internet connections to double bandwidth) -slightly off topic though...
Clustering is usuall used for high availability. where 1 server can do a job but
2 are there so one is reserve.
in practice it's often the case that a lot of applications cannot work in a clustered mode without special setups. two macines cannot write to the same volume unless the file system is a type that allows this.
In general when talking about clustering services (not network load balancing) there are 2 types of setup
active/passive and active/active
in active passive basically a server is sat in reserve waiting to take over in case the first server fails.
in active active both servers are working all the time,
it'd be easy to ramble on, about different setups, but really it's be more usefull to get an idea of what you want to make high availability, then a reply could give some details of what you'll need to do... or what the best clustered approach will be.
(e.g. is this a web server, an LDAP server, mail server, DNS server, database server, proxy server etc)...
-edit, only just noticed the date, probably useless now!
