There are a few routes you could take. Ultimately, having a centrally managed system using Active Directory is going to be far easier for you than trying to jerry-rig the functionality built-in to Professional versions of Windows, but there are options:
Option 1: Buying Windows 7 Professional
BizSpark: If your company is a start-up, you are eligible for the Microsoft BizSpark program, which gives companies access to a wide variety of Microsoft software for extremely reduced prices. You could obtain both Windows 7 Professional and Windows Server licenses through this program.
Volume Licensing: If you need to buy licenses for anywhere from 5 to hundreds of thousands of computers, Microsoft Volume Licensing is the easiest and overall cheapest method. Depending on what type of agreement you make, you can either purchase 30 upgrade licenses just once, and install Windows 7 Pro on all of your machines, or you can purchase a Software Assurance agreement, which entitles you to upgrade (or downgrade) to any version of Windows, even when new ones are released.
Retail upgrade licenses: this is probably the most expensive option, so I would advise against it, but you can just flat-our purchase upgrade licenses. Since you mentioned expense in your question, this is probably not a great suggestion.
Option 1.5: Alternatives to Windows Server, but still buying Windows 7
If you can swing some Windows 7 Pro licenses, but don't want to pay for a Windows Server license (which can be quite pricey), there's also the option of using SAMBA as your domain controller. This gives you most of the functionality you're asking for - essentially, the ability to set up group policy. It runs on Linux, and there are also lots of options for internet filtering which run on Linux as well.
Option 2: Jerry Rigging
If your organization really can't afford Windows 7 Professional licenses (and really, trying to spin your own solution will most likely cost you more long-term because of all the development and support time, but as you wish), you can try to make your own solution. I've done this before for around 10 computers, so it's probably doable with 30, it'll just be painful, and if your organization grows even further, it'll really suck.
You'll want to check out the Group Policy Settings Reference for Windows. This gives a comprehensive list of all Group Policy Settings (which are what you use to restrict users' desktop actions), including - most importantly - the registry settings for these restrictions. There are a few problems though:
- Not every restriction has a registry setting. Some of them are stored in other ways which you can't easily change.
- When you apply these settings manually, there's no easy way to do it for just certain groups on the computer. For each account, you would have to manually import the settings. You could probably write a PowerShell script or something to automate the process, but there are further complications with that.
- When you want to change a setting, you have to do it for every single user on every single computer. Which, again, will be miserable.
So yes, it is possible to get around the limitations of having Home editions of Windows, and hopefully that document will be a good place to start. But I still think it's going to be way more trouble than it's worth.
The other question to ask yourself is, "is it worth all this trouble just so that users can't change their background picture and access the command prompt?" In most small organizations, the answer is probably, "no, it isn't," so if your supervisor is demanding that you implement these restrictions - which more often than not get in the user's way rather than save anybody time - you should really make the argument that if they want to enforce those rules, they'll have to buy the proper tools to make it possible.