If you use Excel 2000 or later, it's relatively easy to save a workbook in HTML as a web document. In fact, Excel supports two types: static documents and interactive documents.
Creating a Static Web Document
After creating your workbook, use the File, Save as Web Page command. Specify what you want to save (a single worksheet or the entire workbook) and click the Save button.
The result will be an HTML document and, possibly, a directory containing ancillary files; the number of such files varies with the complexity of your workbook. These files contain information, such as graphics and macros, that can't be stored in standard HTML format. When you post the HTML file on a Web server, you must include the files in the associated directory. You'll find that the HTML file survives "round-tripping." In other words, if you reopen the HTML file in Excel 2000, every element will be intact.
Creating an Interactive Web Document
Alternately, you may save your workbook (single sheet only) in HTML format with "interactivity." When you open the HTML file in a compatible browser (IE 4.01 or later, not Netscape Navigator), you can interact with the Web page: enter data, recalculate formulas, update charts and pivot tables, and so on. Before you get too excited, however, realize that this feature has some serious limitations. Many common formatting options are not retained, and features like array formulas, macros, and outlining aren't supported.