Hey can anyone please tell me free softwares for converting audio as well as video files from one format to another?

Use VirtualDub for video, GX Transcoder for audio.

Mind you, most audio and video formats use lossy compression, meaning that you lose quality every time you convert.

The post is old but the name on the thread is good.
I'm bad in english but I have to start somewhere

When converting audio I'm using Audacity and Windows sound recorder the most.
However, I don't convert very often and I use to avoid formats like WMA, RA, AU
and similar. WMA might be quite good but the most seems to prefer small filesize
and bad quality. Should be WAV PCM 44,100 kHz stereo + MP3 192 kbps at least.

When converting videos I'm using
Virtual Dub (AVI + MPEG in - AVI out)
TMPGEnc free version (AVI + MPEG in - MPEG1 out)

I hate WMV, MOV and RM videos because they use to have a very bad picture
and sound quality. I know why but hey, it's 2006. Still when I find a good WMV-
clip on the web, I use to convert it to AVI by using the free version 1.0 of the
STOIK Video Converter I think STOIK 1.0 is the best version but it isn't available
for download anylonger. STOIK 2.1.1 is also free but I got errors when I tried it
(fortunately I still have the 1.0 setup). Later I use to convert the stoik-clip
in Virtual Dub with the loseless video codec Huffyuv. (even if I already used
Huffyuv in STOIK, it will not be the same format for some reason). This isn't
recommended for big commercial movies because of the filesize and it will
take all too long. umm... I'll stop here.