Using koraktor's Steam Condenser, you can easily pull this information and use it. 
require_once('steam/db.php');
$_STEAMAPI = "YOURAPIKEYHERE";   // You get this from http://steamcommunity.com/dev/apikey
$playersStr = "";                // This is a comma separated list of profile IDs
                                 // if you don't have those, Steam Condenser has functions to acquire it
$players = array();              // For this example, I'm building an array of players assuming you'll have multiple players returned. 
                                 // You are free to skip this if you are only pulling one back
$url = "http://api.steampowered.com/ISteamUser/GetPlayerSummaries/v0002/?key=$_STEAMAPI&steamids=$playersStr";
$json_object= file_get_contents($url);
$json_decoded = json_decode($json_object);
foreach ($json_decoded->response->players as $player)
{
    $players[$player->steamid]['personaname'] = $player->personaname;     // In game name
    $players[$player->steamid]['profileurl'] = $player->profileurl;       // URL to their Steam Community Page
    $players[$player->steamid]['avatar'] = $player->avatar;               // Small Avatar Icon URL
    $players[$player->steamid]['avatarmedium'] = $player->avatarmedium;   // Thumbnail avatar URL
    $players[$player->steamid]['avatarfull'] = $player->avatarfull;       // Full sized Avatar URL
}    
If you don't have a player's profile ID but do have the Steam ID, you can get the profile ID like this: 
$profile_id = SteamId::convertSteamIdToCommunityId($steam_id);