I know this, I always use the ps3 ip and it works perfectly, but I want to know how to use the webman with localhost, is it possible?
Not sure what you mean...
WMM is a http server & localhost (local domain which resolves as 127.0.0.1) or 127.0.0.1 are loopback interface adresses that automatically point to local servers (ie if you use them in the ps3 browser, they will point to the ps3 servers), they are only meaningful at local level.
Same thing applies to your PC, if you use either of them, you will be calling the PC's servers. You cannot query another device's servers with loopback addresses, at least not unless you set up some kind of redirection system.
To query wMM from your PC you must use an address pointing to the PS3.
The best way is to use the PS3 LAN IP address (192.168.xxx.xxx) but in theory you could also
1. use the router's Internet IP if your router is configured to route Internet based queries on a dedicated port or widely to the PS3 (it makes little sense to use the Internet for a local server request but it is still an option).
2. use a domain name if you have a DNS server configured on your LAN to resolve the name to the PS3 local IP address (it makes little sense to use such a complex setup unless it's already in place for other reasons).
3. etc..
I suggest you tweak your router configuration to set up a static LAN IP address for your PS3 if it's not already the case. You should do it for both WiFi & ethernet if you switch connection type every now and again.
With static adresses, you no longer need to bother finding out the PS3 IP every time you need to query wMM, use FTP or whatever feature querying the PS3 from a PC or smartphone.