Flash and Fireworks are not the same program. What program are you trying to build your site in?
If you are building a Web site in Fireworks, then you can export HTML from Fireworks, but FW is not a code authoring environment. You would not use FW to make later changes to the HTML.
So, can you lay out exactly what program you're using and what steps you're taking? What do you save - what type of file?
I'm sorry, my mistake. I am using Fireworks, not Catalyst, and I'm saving
the files as .png's. I've noticed that this only occurs when I import .psd's
into the website too.
What do you mean by "import .psds into the website?" Are you confusing a Fireworks document with a Web site/page?
A .png file is not a Web page. A Web page consists of an HTML file (which is a text document of code), possibly some images, and perhaps some other resources, such as CSS files, audio files, or videos. HTML files reference the image or other resources, they are not "imported" into it. However, a .psd file is not a normal resource for a Web site.
With Fireworks, you can design your layouts and export images for your Web site. You can also export prototype-ready HTML code of your design that you can show to others for approvals and such. But the Fireworks .png document is not a Web page. A Fireworks document is basically an image, although it is an enhanced format from the standard .png image.
A standard .png image contains only the image (color) data. A Fireworks .png document contains additional data blocks to support layers, slices, vector shapes, etc. Standard .png images, along with .jpg and .gif images, are the supported image formats for the Web. Because a Fireworks document is a .png, however, you can view it in a browser, too. The enhanced information is just ignored. The Fireworks .png is still image data, though, not a functioning Web page.
So what, exactly, are you doing? What version of Fireworks do you have? What OS are you on. It would also help if you posted your working files and maybe someone can see what might be going wrong for you.