OSPF: quagga and HP ProCurve not talking

This question is related to a previous one on OSPF routing.

Based on the advice give to the previous question, I have now made myself a network diagram, identified the backbone area and all other areas and started configuring OSPF on the various routers. All the HP ProCurve 7102dl routers talk to each and that works fine. However, on the intra-area routers, which are all Linux servers, I am using quagga (Version 0.99.10, from debian lenny) and this just won't work at all.

Here are some examples: In one particular area the primary network is 192.168.51.0/24 and both the linux router and the HP router have an interface in that network. The HP router has VPN tunnels to other HP routers and connects the entire subnet to the outside world. Behind the Linux router is another subnet on 192.168.52.0/24. When I look at the OSPF configuration for these interfaces, this is what I get:

Linux router:

uk-swa-bps01# show ip ospf interface eth0
eth0 is up
  ifindex 2, MTU 1500 bytes, BW 0 Kbit <UP,BROADCAST,RUNNING,MULTICAST>
  Internet Address 192.168.51.1/24, Broadcast 192.168.51.255, Area 0.0.0.51
  MTU mismatch detection:enabled
  Router ID 192.168.51.1, Network Type BROADCAST, Cost: 10
  Transmit Delay is 1 sec, State DR, Priority 1
  Designated Router (ID) 192.168.51.1, Interface Address 192.168.51.1
  No backup designated router on this network
  Multicast group memberships: OSPFAllRouters OSPFDesignatedRouters
  Timer intervals configured, Hello 10s, Dead 40s, Wait 40s, Retransmit 5
    Hello due in 6.595s
  Neighbor Count is 0, Adjacent neighbor count is 0

uk-swa-bps01# show ip ospf database
   OSPF Router with ID (192.168.51.1)

            Router Link States (Area 0.0.0.51)

    Link ID         ADV Router      Age  Seq#       CkSum  Link count
    192.168.51.1    192.168.51.1    1335 0x80000016 0xabf6 2

And on the HP router:

bps-test-vpn#show ip ospf interface ethernet 0/2
eth 0/2 is UP, line protocol is UP
  IP address: 192.168.51.254 255.255.255.0, Area: 0.0.0.51
  Router ID: 192.168.51.254, Network type: Broadcast, Cost: 1
  Transmit delay: 1, State: DR, Priority: 1
  Designated Router (ID): 192.168.51.254, Interface Address: 192.168.51.254
  Backup Designated Router (ID): 0.0.0.0, Interface Address: 0.0.0.0
  Timer intervals: Hello: 10, Dead: 40, Retransmit: 5
    Hello due in: 00:00:05
  Number of neighbors: 0, Adjacent neighbors: 0

bps-test-vpn#show ip ospf 0 database 

OSPF router with ID: 192.168.51.254

  Router Link States, Area 0
    Link ID          Adv Router        Age     Seq #         Checksum
    10.10.2.1        10.10.2.1          601    0x80000004    0xECAD
    10.176.1.33      10.176.1.33       1526    0x80000086    0xAAE1
    10.181.1.1       10.181.1.1         826    0x8000009A    0x56EF
    192.168.51.254   192.168.51.254     819    0x8000001D    0x0B13

  Summary Net Link States, Area 0
    Link ID          Adv Router        Age     Seq #         Checksum
    10.171.0.0       10.10.2.1          825    0x80000001    0x2867
    10.171.0.0       10.176.1.33       1520    0x80000001    0x3990
    10.181.0.0       10.181.1.1        1226    0x80000009    0x4989
    10.181.1.0       10.181.1.1        1226    0x80000032    0xD9D1
    192.168.51.0     192.168.51.254     824    0x80000016    0xF915
bps-test-vpn#show ip ospf 0.0.0.51 database 

OSPF router with ID: 192.168.51.254

  Router Link States, Area 0.0.0.51
    Link ID          Adv Router        Age     Seq #         Checksum
    192.168.51.254   192.168.51.254     845    0x80000009    0xFD79

  Summary Net Link States, Area 0.0.0.51
    Link ID          Adv Router        Age     Seq #         Checksum
    0.0.0.0          192.168.51.254     610    0x80000005    0x15AA
    10.10.1.40       192.168.51.254     835    0x80000001    0x87FF
    10.10.1.44       192.168.51.254     830    0x80000001    0x6919
    10.10.1.52       192.168.51.254     835    0x80000001    0x0F6C
    10.10.1.72       192.168.51.254     844    0x80000001    0x3C2C
    10.10.1.76       192.168.51.254     835    0x80000001    0x1E45
    10.171.0.0       192.168.51.254     830    0x80000001    0xA269
    10.181.0.0       192.168.51.254     830    0x80000001    0x34CC
    10.181.1.0       192.168.51.254     830    0x80000001    0x17EB

Clearly OSPF is enabled on both sides on the interfaces that are in the 192.168.51.0/24 subnet, yet they don't talk to each other, because otherwise I would be getting some OSPF routes on the Linux Box. But I am not. So what am I doing wrong? I have tried all sorts of things, but I am not making any headways. Any advice would be appreciated. If you need additional info, just ask and I'll edit my post.