Edit to address the actual question: Before bringing this up with the client, here are some things to consider:
- What is your relationship with the client? Is this a one project deal, or do you hope to continue working for them? Either way, do you want to get a good reference from them? Are you a long established service provider with a high level of trust, or a new face who has yet to prove themselves? How would they respond if you suggest that they change? Would they mind switching web hosts?
- How comfortable are you working with Windows in general? Can you can use it with moderate skill and comfort?
- What is your time frame for project completion? How long would it take to find a new hosting service and get set up? How will this impact your scheduled completion?
Ultimately, if you decide to raise the issue, the client has to decide whether they want to move to a new hosting company. Some factors to consider there include:
- How long have they been with this host? How good or bad is the relationship between your client and their hosting company. What contractual obligations are in place between them? Would your client have to pay to leave?
- After you finish the initial development, who is going to maintain and administer the system (you or someone at the client company), and which system do they know?
Now, if you want to use Windows, I'll mention that, in addition to XAMPP, the WAMP server, which will run on just about any modern version of Windows. I used it for a class (where it was required), and then on a development system for a project at work that ultimately ran on a Linux server. Both ran Windows XP. I don't recall needing to make any changes when copying the PHP from Windows to Linux, although I did stay away from any functions which would have been platform dependent. FWIW, I found WAMP very easy to set up, administer, and use.