What’s the difference between Clustering and Load Balancing

While not familiar with Windows NLB (other than fearing it from a network guy's perspective), what it sounds like you're doing is bridge looping your network. This could turn out quite bad.

Consider:

Server1---nic1---subnet1---nic1---Server2
       |--nic2---subnet2---nic2--|

This is a bridge loop and is bad. Normally, you'd be setting up a scenario where you will bury your network a traffic storm. An NLB expert may contradict me, and it's likely they will be right, as I'm not familiar enough with NLB functionally to be certain. However, simply bridging these connections is not a good idea, neither from a moving packets perspective, nor a broadcast domain one.

There is a big difference between a failover cluster and a network load balanced cluster. For IIS, you want to implement an NLB cluster. Both will be active all the time. For SQL you'll want to implement a failover cluster. Achieving the levels of availability that you are hinting at is not as simple as throwing in a little hardware and installing the operating systems.

A failover cluster will need some sort of shared storage like direct attached SAS or a SAN (I prefer iSCSI). All of this can be accomplished in a virtual environment by clustering 2 servers running 2008R2 (enterprise or higher) with Hyper-V (at least 4 nics. 2 for SAN, 1 for NLB and one for other comm). These would be attached to the SAN switches which in turn connect to the SAN. Then both would be connected to the front end switches (NLB and other). Then you can create the NLB cluster as virtual machines and the SQL failover cluster as virtual machines.

Now to add some more infrastructure. You'll need domain controllers (2 physical boxes) and a backup server. All told you'll be looking in the range of $150K and up along with someone who really knows what they're doing. Achieving high availability isn't cheap.

Oh, and don't forget about redundant power and cooling. Have a disaster recovery (DR) and business continuity (BC) plan.

Just thought about an alternative. Have your site hosted with a 99.99% service level agreement (SLA). Make sure it's local and take a tour of the data center. Might be cheaper in the long run considering the human cost.