Like the other posters mentioned, it's not the hardware that is causing your problems (more than likely not at least), its the size of your user base vs the quality of the queries. We use SQL Sentry at my office and its really good at providing detailed stats about the deadlocks, the offending procedures and even the code segments all piled into a nicely displayed gui that is easy to navigate.

You can do it without the expensive software, but I totally recommend it. I'm a visual person and it's helped my team pin point a lot of areas for improvement and we operate at about 1600 transactions/s on a low to mid range of our peak.

Only other thought I have is the tempdb, any issues there? every filled it up? is it running on it's own disk? can it?

Sounds like your hands are tied due to the commercial products you're hosting, but if you can trace the problem to the software, you could have a case that you could bring to the support teams of your respective products. Remember, they need your business! Most vendors are quite helpful so long as you present the evidence and show that you're willing to work with them. Good luck!