TTL=64 = *nix - the hop count so if your getting 61 then there are 3 hops and its a *nix device. Most likely Linux.
TTL=128 = Windows - again if the TTL is 127 then the hop is 1 and its a Windows box.
TTL=254 = Solaris/AIX - again if the TTL is 250 then the hop count is 4 and its a Solaris box.
OS Version Protocol TTL
AIX TCP/UDP 60,30
AIX 3.2, 4.1 ICMP 255
BSDI BSD/OS 3.1 and 4.0 ICMP 255
Compa Tru64 v5.0 ICMP 64
DEC Pathworks V5 TCP and UDP 30
FreeBSD 2.1R TCP and UDP 64
FreeBSD 3.4, 4.0 ICMP 255
FreeBSD 5 ICMP 64
HP-UX 9.0x TCP and UDP 30
HP-UX 10.01/11 TCP and UDP 64/255
Irix 5.3/6.x TCP and UDP 60
Irix 6.5.3, 6.5.8 ICMP 255
MPE/IX (HP) ICMP 200
Linux 2.0.x kernel ICMP 64
Linux 2.2.14 kernel ICMP 255
Linux Red Hat 9 ICMP and TCP 64
MacOS/MacTCP 2.0.x TCP and UDP 60
MacOS/MacTCP X (10.5.6)ICMP/TCP/UDP 64
NetBSD ICMP 255
Netgear FVG318 ICMP and UDP 64
OpenBSD 2.6 & 2.7 ICMP 255
OpenVMS 7.1-2 ICMP 255
OS/2 TCP/IP 3.0 64
OSF/1 V3.2A TCP 30/60
Solaris 2.5.1, 2.6, 2.7, 2.8 ICMP 255
Solaris 2.8 TCP 64
Stratus TCP_OS ICMP 255
Stratus TCP_OS (14.2-) TCP and UDP 30
Stratus TCP_OS (14.3+) TCP and UDP 64
Stratus STCP ICMP/TCP/UDP 60
SunOS 4.1.3/4.1.4 TCP and UDP 60
SunOS 5.7 ICMP and TCP 255
Ultrix V4.1/V4.2A TCP 30/60
Ultrix V4.2 - 4.5 ICMP 255
VMS/Multinet TCP and UDP 64
VMS/TCPware TCP/UDP 60/64
VMS/Wollongong 1.1.1.1 TCP/UDP 128/30
VMS/UCX TCP and UDP 128
Windows for Workgroups TCP and UDP 32
Windows 95 TCP and UDP 32
Windows 98 ICMP 32
Windows 98, 98 SE ICMP/TCP 128
Windows NT 3.51 TCP and UDP 32
Windows NT 4.0 TCP and UDP 128
Windows NT 4.0 SP5- 32
Windows NT 4.0 SP6+ 128
Windows NT 4 WRKS SP 3, SP 6a ICMP 128
Windows NT 4 Server SP4 ICMP 128
Windows ME ICMP 128
Windows 2000 pro ICMP/TCP/UDP 128
Windows 2000 family ICMP 128
Windows Server 2003 128
Windows XP ICMP/TCP/UDP 128