I agree with seacue - with Excel 97, if you have the Format/Cells/Number set to 'number' and have highlighted the second option down under 'negative numbers' (1234.10 in red on mine) it will do that.
Change it to the top one (-1234.10 in black) and see.
Regarding the 'plus' numbers, I'm pretty sure Excel uses the standard notation of dropping the '+'. It still counts as a '+' though. Check the Help files?