Haven't checked because I'm on Linux right now, but is it possible that WFB can save/export files as xls instead of csv?

Not at this time.

I'm probably way off base but don't you need something like Microsoft Excel Web App to make this work across browsers and sites?

That's what I said earlier. I tested a form on my server and when I go to the form-resluts.csv the pop up window ask if I want to open it with Excel. I have it on my win7 64 bit machine.

I tried with a published form of my own in four different browsers and the .csv file consistently downloads and opens nicely in Excel. The only difference between browsers is that, while Firefox, Opera and IE9 pops up the question about which program (default: Excel) to open with, Chrome simply downloads the .csv file without automatically opening it.

Since it is only a question of a simple download of a .csv file, which is a well-defined entity, I don't quite understand what you mean when you say that others get a "raw data file" and that it has "a lot of html across the page". This implies that they are downloading the wrong file of the wrong type.
The .csv file does not contain any html, so I don't know where that could possibly come from.

The default path to the .csv file is:

www.[domain.com]/[form-name]/storage/csv/form-results.csv

Does the path you give to your client and others look like that - complete with the .csv file extension?

Kathy,

I looked back at a previous thread of yours on essentially the same topic. When I tried one of your links there - but renaming the .txt file ".csv" since the ".txt" one does not exist - the file did not download, but just opened in the browser window. This would indicate some kind of formatting error in the file. You also mentioned that you had tried various things to make it work, including renaming the file. Did you by any chance start out creating a .txt file manually in the csv folder (rather than letting the WFB create it for you) and then renamed it with a .csv extension? This would probably confuse the formatting of data in the file...

Here is what I suggest you do:
Delete any file(s) you have in the /storage/csv folder on your server. Then let the program create a new .csv file as you submit a couple of test cases.