A little confused here, you say "i installed avast_free_antivirus_setup on WIN7 32bit." but you also say "it is newly reformated HDD with XP." ?
The avast installation file is compatible with XP, Vista and Win7 (plus win8) for both 32 and 64bit OS version of those, so it shouldn't really matter what OS you have of those avast should be OK.
I take it you mean .net framework and the answer is no.
Do you have a firewall installed, if so what ?