Since you are seeing some parts but some are showing scrambled it is quite difficult to answer.Once I had the same problem.If you are using the Firefox go to the View->Character Encoding and make sure that Unicode(UTF-8) is selected.If you are on other browser just try to change he encoding to unicode.When I change it to other font it shows the scrambled so this might fix it.

For writing in unicode if u wanna do online u can use the site provided by freedom writer and google also provides this service at http://www.google.com/transliterate/ .So that u have to write there and copy and paste it to other place.

But if u wanna be able to write in any textbox, microsoft word or anywhere in your computer then I think u can download the Google IME for nepali language from here.

http://www.google.com/ime/transliteration/

Install it and it will show the input language u are using on your taskbar.You can change back and forth between nepali and english.Using this u can write in nepali langauge anywhere just by changing the input language.So that you don't have to write somewhere and copy and paste it to another place.It also displays a nice character layout which would help the starters who are not accustomed to roman phonetic style writing.Pretty handy tool.

Thx