Problem with Wireless Card

Hello, everyone!
Firstly I wanna notice that english is not my native language, sorry for my mistakes.

Before 6 - 7 days I bought a PC with wireless lan (RP-WP5122E WL-N PCI-E ADAPTER). I have and laptop, too. My router is Linksys WRT160NL. The laptop have a wireless card with G standart. On speed test makes 14 - 17 Mbps download, which is normal. When I try to download something on my PC maximum speed is 400 - 600 kbps, on speed test is 2 - 4 Mbps. When I connect my PC with cable to my router speed was 10MB/s (80 - 85 Mbps). I try to change channels on wireless network, but there is no change. I downloaded the latest drivers for this WLAN, but the speed is the same. I change the slot on the mainboard and to flash the firmware on my router, but there is no change. At last I change the possition of antenas. The best speed now is 20 - 25 Mbps, but it's too far away of these ~80Mbps on LAN. I'm a out of a ideas!

Please help.

Best regards from Bulgaria

P.S - I forgot to notice that the distance between PC and router is no more than 5 - 6 meters. There is a wall too, but it isn't thick, only 10 - 15 centimeter.

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RP-WP5122E WL-N PCI-E ADAPTER

• Standards
IEEE 802.11n, IEEE 802.11g, IEEE 802.11b
• Interface
Complies with PCI Express Base Specification Revision 1.1
• Antenna
Two 2dBi Detachable Antenna
• Frequency band
2.412GHz-2.4835GHz
• Security
64/128-bit WEP, WPA, WPA2
• Data Transfer Rates
IEEE 802.11b: 1, 2, 5.5 and 11 Mbps
IEEE 802.11g: 6, 9, 12, 18, 24, 36, 48, 54 Mbps
IEEE 802.11n: up to 300Mbps
• Modulation
OFDM, CCK
• Transmit Power
802.11n: 13dBm
802.11g: 14dBm
802.11b: 18dBm
• Range Coverage
Indoor 35~100 meters
Outdoor 100~300 meters