I want to generate a BIP32 version number for Namecoin and other altcoins I want to make a BIP32 wallet for Namecoin and other alt coins. I just need to figure out how to generate a a public and private version number so that the BIP32 extended key prefix is something that makes sense like "nprv" for a Namecoin private key and "npub" for a public key.

Been struggling with this one
I can not tell you really how you generate them, but to partially answer your question, here is a list of known Bitcoin and Altcoin prefixes, including Litecoin and Darkcoin:

EXT_SECRET_KEY, EXT_PUBLIC_KEY # Network                 : Prefixes
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0x0488ADE4,     0x0488B21E     # BTC  Bitcoin    mainnet : xprv / xpub
0x04358394,     0x043587CF     # BTC  Bitcoin    testnet : tprv / tpub
0x019D9CFE,     0x019DA462     # LTC  Litecoin   mainnet : Ltpv / Ltub
0x0436EF7D,     0x0436F6E1     # LTC  Litecoin   testnet : ttpv / ttub
0x02FE52F8,     0x02FE52CC     # DRK  Darkcoin   mainnet : drkv / drkp
0x3A8061A0,     0x3A805837     # DRK  Darkcoin   testnet : DRKV / DRKP
0x0488ADE4,     0x0488B21E     # VIA  Viacoin    mainnet : xprv / xpub
0x04358394,     0x043587CF     # VIA  Viacoin    testnet : tprv / tpub
0x02FAC398,     0x02FACAFD     # DOGE Dogecoin   mainnet : dgpv / dgub
0x0488ADE4,     0x0488B21E     # VTC  Vertcoin   mainnet : vtcv / vtcp
0x02CFBF60,     0x02CFBEDE     # BC   Blackcoin  mainnet : bcpv / bcpb
0x03A04DB7,     0x03A04D8B     # MEC  Megacoin   mainnet : mecv / mecp
0x0488ADE4,     0x0488B21E     # MYR  Myriadcoin mainnet : myrv / myrp
0x0488ADE4,     0x0488B21E     # UNO  Unobtanium mainnet : unov / unop
0x037A6460,     0x037A689A     # JBS  Jumbucks   mainnet : jprv / jpub
0x0488ADE4,     0x0488B21E     # MZC  Mazacoin   mainnet : xprv / xpub


I've taken them from the pycoin api implementation which supports HD wallets.
https://github.com/richardkiss/pycoin/blob/master/pycoin/networks.py