U should hook outcoming RPC_DialogResponse and read parameters:
WORD dialogID, BYTE buttonID, WORD listboxItem, BYTE strLen, char[] text
bool CALLBACK incomingRPC(stRakNetHookParams *params)
{
WORD wDialogID;
BYTE bButtonID;
WORD wListBoxItem;
char szInputResp[128+1];
unsigned char iInputRespLen;
params->bitStream->Read(wDialogID);
params->bitStream->Read(bButtonID);
params->bitStream->Read(wListBoxItem);
params->bitStream->Read(iInputRespLen);
params->bitStream->Read(szInputResp, iInputRespLen);
szInputResp[iInputRespLen] = 0;}