Once TrueType fonts are installed properly, there is no problem using them in Abiword, GNumeric or KOffice. However, StarOffice needs Type 1 fonts. (I hear the latest StarOffice supports TrueType fonts?). You can expect Type 1 Tamil fonts to be available shortly:-).
For receiving and sending email, KMail works well with TrueType fonts. You should also be able to use PINE with Sivaraj's console fonts and utils.