The provider confirmed to me that the ip remains static and i get it assigned as 124.123.163.164/255.255.192.0 Default Gateway:124.123.168.1 and some DNS entries.
Because this is a very different situation than what I originally thought we were talking about, I've completely replaced my previous answer. If anyone is curious what I deleted, the previous revisions are still out there, of course.
@Anirudh
While I'm not very skilled at such things, I did try to do a whois.net lookup of the IP they gave you, 124.123.163.164. It appears to be registered with "Asia Pacific Network Information Centre" in Milton, Australia. But the contact info points to "Beam Telecom", "Beam Cable System", and/or "Beam Telecom Pvt Ltd", 8-2-610/A, Road No - 10 Banjara Hills, Hyderabad, India.
The subnet mask they gave you, 255.255.192.0, implies that your IP and the 16,382 (?) other IPs in the range 124.123.128.1 to 124.123.191.254 are on the same subnet of the larger Internet. In other words, all these public IPs are in some sense "local" to your IP. That's a relatively big subnet which I find surprising. It makes me wonder how their network actually functions. Oh, well.
What you appear to have is a one static IP which is on the public Intenet. In other words, you don't have a local LAN at all, just an IP which gives you direct, unfiltered ... and unprotected! ... access to the Internet. This would also mean there is no DHCP server so you would need to manually enter the IP configuration data ... the IP address, the default route, and the DNS servers ... into the one computer you could connect to the Internet using this IP address.
So, yes, I would recommend you obtain another router and put it between you and the free rolling chaos which is the unfiltered public Internet. Put your systems on a local LAN behind a router which uses (at least) NAT, SPI and DHCP.
You would then enter the one static IP you were given as the WAN information for the router, connect the router via its WAN port to the ethernet port from your ISP, and then connect your systems to the router LAN ports. Your computer(s) would then have local LAN IPs assigned to them by the router's DHCP.
I would also recommend ignoring the DNS servers your ISP gave you and going with one of the public DNS providers such as OpenDNS or Google DNS. Maybe it's just me, but I like having even a small bit of extra filtering between me and the hoards of malicious sites out there these days.
As for the router itself, there are two ways you could go.
You could, as you mentioned, obtain a home router which includes wireless.
But you could also use a wired home router, connect your Beetle to it, and then use the Beetle for wireless access. This is what I thought you were trying to do in my previous answers.
I mention this as an option because you might know someone who has a wired router they no longer use which you could re-purpose. Depending on your situation, it might be a quicker or cheaper solution for you.
The important thing is to get a router, either wired or wireless, which gives you some isolation from the public Internet by using NAT plus "stateful packet inspection" (SPI) to create your own LAN. The router's DHCP would also save you the hassle of entering static configuration info and would allow multiple computers to use/share your Internet access at the same time.
I'd been puzzling over how you could get it to work, when I remembered Connectify. If you can get your hands on a wireless USB it should work perfectly for your situation instead of having to deal with that router.
I'm not sure there's a good way to connect the router like that, there's too many variables between the Siemens device and the cable modem. You might be able to connect the cable modem to a LAN port in the router, shut off DHCP in the router, give the router a static IP that's on the same subnet as the modem but not taking the modem's IP, and see if it will route packets appropriately between your computer and the cable modem. If you don't even get DHCP from the cable modem, that's a bad sign. You could try setting a static IP address for your computer and manually assigning the cable modem as the gateway, but it might just ignore your PC if it doesn't go through DHCP first (I know mine does.) The router might get confused too if it's looking for WAN, so setting to bridged mode might help. It all really depends on how the cable modem and router operate, and I'm not sure how much of this is standards based. Might end up being a lot of trial and error...
Connectify though is really easy, but you'll need XP with SP3, and you'll want to run in Ad-hoc mode anyway.
Best Answer
If your ISP can send multiple IPs through the circuit and you get a cheap switch, then you'd pull IPs in parallel by static assignment, keep in mind there is no firewall and your IPs are 100% public with this option. If you turn off DHCP and NAT, then you should be able to use that ADSL modem/router as the switch for this scenario.
If your ISP is only sending you one IP and you can't get more than you must use DHCP/NAT, hence you must use a router.