Dr.TCPでもNet Tuneでも設定が反映されないよ〜
Win2K＋RasPPPoE0.96
設定後、再起動はちゃんとしたよ。
再起動後にDr.TCPとNet Tuneを起動すると入力した数値が出てくる。

TCP options string = 020405b4010303000101080a0844056f00000000
MTU = 1500
MTU is fully optimized for broadband.
MSS = 1460
Maximum useful data in each packet = 1448, which is less than MSS because of Timestamps, or other TCP/IP options used.
Default Receive Window (RWIN) = 8760
RWIN Scaling (RFC1323) = 0 bits
Unscaled Receive Window = 8760
RWIN is a multiple of MSS
Other values for RWIN that might work well with your current MTU/MSS:
513920 (MSS x 44 * scale factor of 8)
256960 (MSS x 44 * scale factor of 4)
128480 (MSS x 44 * scale factor of 2)
64240 (MSS x 44)
bandwidth * delay product:
Your RcvWindow limits you to: 350.4 kbps (43.8 KBytes/s) @ 200ms
Your RcvWindow limits you to: 140.16 kbps (17.52 KBytes/s) @ 500ms
Consider increasing your RWIN value to optimize TCP/IP for broadband.
MTU Discovery (RFC1191) = ON
Time to live left = 55 hops
TTL value is ok.
Timestamps (RFC1323) = ON
Note: Timestamps add 12 bytes to the TCP header of each packet, reducing the space available for useful data.
Selective Acknowledgements (RFC2018) = OFF
IP type of service field (RFC1349)= 00000000