Indu:
As far as I know the only thing you can do is change the order of your parameters.
A trick that you may want to try (because the parameter entry field will default to the size of the largest value) is set a default value and add a lot of spaces. It may not look to pretty and I haven't tried it myself so it is just a suggestion.
I would love it if we could modify the size of the parameter fields as well, hopefully they are making this happen in 2008.
Sorry, and I hope this helps a little bit.