It sounds like you're trying to get a job as a copywriter. Obviously, your portfolio will look much more professional if you use software such as Photoshop or InDesign. However, these products come with steep price tags and learning curves.

On the other hand, once you have a terrific looking portfolio, the problem solves itself. You won't need those tools, as the ads (brochures/ newsletters/ flyers/ web sites) will have been done by a professional graphic designer.

Consider hiring yourself at a fairly low rate to a designer with a portfolio you really like. After partnering on some projects, you'll have a portfolio you can take anywhere.

Once you're working as a copywriter, you can communicate your concept to the designer/design team using words alone (e.g., "Photo of screaming teen in messy room"), and then write your headline and body copy.

Save your paychecks, and then when you're ready, buy a Mac. You'll be glad you did.

Have fun,
Rex