Many browsers see your tab as being equal to one space. Some browsers will see a long string of spaces as one space. Avoid structuring your page using spaces and tabs. If you want to present information in columns, programs like Word97 will let you generate tables. These will save as rows and columns when you save your document as html.
Tables are an excellent way of organizing information into rows and columns.
Most html composers will make tables for you. A lot of people organize their lists with indentations, usually done with tabs. This looks good in your word processor, but not in a browser. This is just the way it works. In the browser, this same keystroke results in a space between the lines.