There is no ASCII character 144. ASCII only runs up to 127.
So did you mean Windows-1252 character 144? That happens to be a non-assigned character. (See character map).
So the system prints the symbol for a non-existent character, which happens to be a rectangle in the font used on your XP machine, and nothing in the font on your Win 7 machine.
To display a proper rectangle, take a look at the geometric shapes in the Unicode region U+25A0..U+25FF. U+25AF looks like it's the one you want.
Edit
I see you're using VB.Net now, so forget about ASCII and Windows-1252. VB.NET uses UTF-16 internally, so you don't have to be afraid that you can't display a certain Unicode codepoint. Just write chr(&H25AF)