Haven't tried it yet, but seems feasible as far as I can tell you could build a spare computer to be used as a local area network ram drive.

After looking around and figuring out ratios number on bits to bytes it looks like
1000mbps=125MB/s
1000mbps (full duplex ie teaming)=250MB/s
2000mbps 250MB/s
2000mbps (full duplex)=500GB/s
10gbit= 1.25GB/s
10gbit (full duplex)=2.5GB/s
another thing to take into consideration though is the NIC connection bandwidth itself
PCI NIC=133MB/s
PCI-Express x1=250 MB/s
PCI-Express x4=1GB/s
I'm not too sure if or what bandwidth for onboard 1000-2000mbps LAN is, but I'd guess the same as PCI or maybe higher if we're lucky hard to tell either way it would be depends on both computers so any bottlenecks between them would slow the other down, but 1000mbps doesn't saturated PCI bandwidth and equates to 125MB/s which any way you look at it is fast.

The current 4GB setup I'm thinking of would be $244.94 + shipping & handling which I could get even a little cheaper with a different cpu, ram, and board combination, but would lose a bit of future expandability and would run slightly slower if I intended to make it multipurpose system.

ECS AMD690GM-M2 AM2 AMD 690G Micro ATX AMD Motherboard - Retail
Item #: N82E16813135049
Return Policy: Standard Return Policy
$20.00 Mail-in Rebate
$64.99

TRENDnet TEG-PCITXR 10/ 100/ 1000/ 2000Mbps PCI Copper Gigabit Network Adapter - Retail
Item #: N82E16833156139
Return Policy: Limited 30-Day Return Policy
$15.99

TRENDnet TEG-S50TXE 10/20/100/200/2000Mbps Copper Gigabit Switch - Retail
Item #: N82E16817111480
Return Policy: Limited 30-Day Return Policy
$33.99

pqi POWER Series 2GB 240-Pin DDR2 SDRAM DDR2 800 (PC2 6400) Desktop Memory Model MAD42GUOE - Retail
Item #: N82E16820141300
Return Policy: Memory (Modules, USB) Return Policy
-$3.00 Instant
$79.98
$73.98
($36.99 each) [2x2GB=4GB]

AMD Athlon 64 X2 3600+ Brisbane 1.9GHz Socket AM2 65W Dual-Core Processor Model ADO3600DDBOX - Retail
Item #: N82E16819103046
Return Policy: Processors (CPUs) Return Policy
$55.99

Subtotal: $244.94 + shipping & handling

Link http://en.wikipedia.org/wiki/DDR2_SDRAM
ddr2 400 starts out at a transfer rate of 3,200 MB/s with ddr2 1066 running 8,533 MB/s
So even a 10gbit connection will only give you a maximum of 1.25 GB/s or 1/3 of ddr2 400 speed. Count in network overhead and network latency and you'll probably see 800MB/s. Nowhere near whats needed to effectively run a modern computer for any kind of use.

Use iperf to see your throughput numbers, I wouldn't even consider this.