Ok, here's what you need to do. Matt101's suggestion might work if the PS3 and PC had another source to get an IP address from (i.e. a DHCP server) but since you want to make a direct connection (not sure why, it won't be any faster) you need to set the IP Address of both your PC and PS3 manually. If you don't want to do this just leave your router connected to the network and connect to the PS3 to it so they all get IP addresses.
For a direct connection, you need to manually set your PS3's IP first. Go to Settings and then Network Settings. Choose "Manual Connection" and then move through the settings choosing the default options until you get to the IP Address section. Put in an IP address of 192.168.1.100 with a Subnet Mask of 255.255.255.0. You can put anything you want in for the gateway and DNS server, these don't matter for what you are doing. Proceed through the settings and save.
Now move on to your PC. Assuming you are a windows user, access your network adapter's properties area and highlight TCP/IP v4 and click "Properties". Set the IP address to Manual and enter 192.168.1.101 with a Subnet Mask of 255.255.255.0. You can enter anything you want for the gateway and DNS, as these don't matter for the direct connection. NOTE: You will NOT be able to access the internet when doing this.
Start an FTP server on your PS3 (i.e. MultiMan) and then open FileZilla and Quick Connect to 192.168.1.100. You will now be connected directly to you PS3.
If you don't understand these instructions just use a DHCP server like your local router and connect through it.