Earlier I am using MS Outlook-2007 but now I am using Windows Live Mail which is inbuilt with windows 7 .

I want my old mails in WLM client but its not supported to .PST file. I am download some 3ed party converters which converts .pst to .eml but the issue is they all are demo versions please give me proper solution which is free.

I am looking forward for your positive response.

Use a decent client rather than the updated outlook express.
Thunderbird is your best bet.
Fast, free and extendible.